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UNlVERitTY OF CALIFORNIA 

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GEOLOGY OF NORTHERN CALIFORNIA 



EDGAR H. BAILEY, Editor 
United States Geological Survey 



BULLETIN 190 

California Division 

of 

Mines and Geology 

Ferry Building, San Francisco 

1966 




LIBRARY 

UNIVERSITY -^F CALIFORNIA 



Vf j'i*' State of California 
^^ /»*EDMUND G. BROWN, Governor 

Uji* ^^® Resources Agency 

'pf^i HUGO FISHER, At/minisfrator 

,'^5'-; Deportment of Conservation 

; ? IAN CAMPBELL, Direclor 



m 



i':^. DIVISION OF MINES AND GEOLOGY 



^%^^, 



IAN, CAMPBELL, Hale Geologiil 

BULLETIN 190 



Price $6.00 /} 



CONTENTS 

PREFACE 



SCOPE AND ARRANGEMENT OF THE BULLETIN _ 1 

CHAPTER I. INTRODUCTION _ 3 

State geo/og/'c maps of California — o brief history, 

by Charles W. Jennings 5 

The first geologic maps — 1826, 1850 5 

Maps of the railroad explorations , 7 

Map of the country west of the Mississippi River — 1857 8 

France explores California and Nevada — 1867 8 

Ninth census map — 1872 _ _ _ 10 

The missing Whitney Survey map— 1873? 10 

Marcou's map of California — 1883 _ 12 

Hitchcock's maps of the U.S.— 1887-.-_ _ 12 

First large-scale statewide geologic map of California — 1891 14 

Reconnaissance geologic map of California — 1916 14 

Fault map of California — 1923 15 

O. P. Jenkins geologic map of California — 1938 _ _. 15 

New geologic atlas of California 16 

References . 16 

CHAPTER II. KLAMATH MOUNTAINS PROVINCE 17 

Geology of the Klamath Mounta/ns province, by William P. Irwin 19 

Subjacent rocks 21 

Eastern Klamath belt 21 

Central metamorphic belt 21 

Western Paleozoic and Triassic belt 21 

Western Jurassic belt 24 

Ultramafic rocks 26 

Granitic rocks 27 

Superjacent rocks 28 

Quaternary deposits 30 

Structure 31 

References 37 

Metamorphic and granitic history of the Klamath Mountains, 

by Gregory A. Davis — 39 

Eastern Paleozoic subprovince 39 

Central metamorphic subprovince 41 

Western Paleozoic and Triassic subprovince 41 

Seiad Valley — Condrey Mountain — Fort Jones area 44 

Western Jurassic subprovince ■ 45 

Regional metamorphism and ultramafic intrusions 46 

Granitic intrusions 47 

Conclusions ^° 

References 50 

Economic deposits of the Klamath Mountains, by John P. Albers 51 

Deposits found in ultramafic igneous rocks _ 51 

Chromite " 

Asbestos -_ . 54 

Nickel ; 54 

Deposits chiefly in metamorphosed sedimentary and volcanic rocks 

and inferred to be genetically related to granitic rocks 54 

Gold 54 

Iron 57 

Massive sulfides and replacement veins 58 

Silver _ ^ 

Deposits inferred to be associated with late volcanic activity 61 

Quicksi Iver 61 

Deposits concentrated by sedimentary processes -- 61 

Manganese — 61 

References " 



CONTENTS-Continued page 

CHAPTER III. CASCADE RANGE, MODOC PLATEAU, AND GREAT 

BASIN PROVINCES 63 

\ 

Geology of fhe Cascade Range and Modoc Plateau, 

by Gordon A. Macdonald 65 

Cascade Range 66 

Cretaceous and early Tertiary sedimentary rocks _ 67 

Western Cascade volcanic series .._ 69 

Tuscan Formation 71 

High Cascade volcanic series 71 

Mount Shasta . 74 

Lassen Peak region 76 

Medicine Lake Highland 83 

Lava Beds National Monument _ 87 

Modoc Plateau 89 

Cedarville series 89 

Pliocene rocks other than Warner Basalt 90 

Warner Basalt 91 

Pleistocene and Recent volcanic rocks other than Warner Basalt 93 

Quaternary sedimentary rocks _ 94 

Structure .._ 94 

Hydrology 95 

References 95 

Economic mineral deposits of fhe Cascade Range, Modoc Plateau, and 
Great Basin region of northeastern California, 
by Thomas E. Gay, Jr. 97 

Metallic mineral commodities 97 

Copper _ 97 

Gold 97 

Quicksilver _ _ 100 

Uranium _ 100 

Nonmetallic mineral commodities __ _ 100 

Calcite (optical) 100 

Clay _ 101 

Coal 101 

Decorative stone _... 101 

Diatomite ._ 101 

Hot springs _ 1 01 

Limestone 101 

Obsidian _ 1 03 

Peat 1 03 

Perlite _ 103 

Petroleum and gas _ _ 103 

Pozzolan ..„ _ 103 

Pumice and pumicite 103 

Salt 103 

Sand and gravel 103 

Stone, crushed 104 

Volcanic cinders 104 

References 104 

CHAPTER IV. SIERRA NEVADA PROVINCE..... 105 

Geology of the Sierra Nevada, by Pool C. Bateman 

and Clyde Wahrhaftig 107 

General geologic relations 107 

Milestones of geologic study 107 

Prebatholithic "framework" rocks _ Ill 

Paleozoic rocks Ill 

Mesozoic stratified rocks 113 

Structure of the "framework" rocks 115 



CONTENTS-Continued 



The batholith 

Mafic rocks 


116 

116 


Larger features of the granitic rocks 


117 



Textures of the granitic rocks _ _ 119 

Mafic inclusions . _ 119 

Primary foliation and lineation 121 

Compositional zoning within plutons 121 

Regional joints 121 

Speculations on the origin of the batholith 122 

Depth of erosion since Mesozoic plutonism 125 

The Superjacent series _ 128 

Upper Cretaceous rocks (Chico Formation) 128 

Lower Eocene deposits of the foothills ___ 129 

lone Formation ,. __ _. 129 

Prevolcanic gravels 1 33 

Volcanic formations and intervoiconic gravels of the northern 

Sierra Nevada _.._ 136 

The Tertiary landscapes of the northern Sierra Nevada 139 

Cenozoic volcanic rocks of the southern Sierra Nevada 139 

Late Cenozoic deformation and erosion in the northern Sierra 

Nevada _ 145 

Late Cenozoic deformation and erosion in the southern Sierra 

Nevada 149 

j^ Glaciation 158 

-^Summary of geologic history _ 164 

References 169 

Geology of the Taylorsville area, northern Sierra Nevada, 

by Vernon E. McMath 173 

Main stratigraphic sequences 175 

Revision of Paleozoic stratigraphy 177 

Description of the sequences 178 

Shoo Fly Formation 178 

Pyroclastic sequence . 179 

Grizzly Formation 179 

Sierra Buttes Formation 179 

Taylor Formation 179 

Peale Formation 179 

Arlington Formation 179 

Goodhue Greenstone 179 

Reeve Formation 1 80 

Robinson Formation 180 

Age of the pyroclastic sequence 180 

Regional relations of the pyroclastic sequence 180 

Triassic sequence _ 181 

Jurassic sequence 181 

Acknowledgments 1 82 

References 1 83 

Tertiary and Quaternary geology of the northern Sierra Nevada, 

by Cordell Durrell 185' 

Previous work . 1 85 

Geology . . 1 85 

I ntroduction 1 85 

Stratigraphy 1 85 

Cretaceous 1 85 

Eocene 1 87 

"Dry Creek" Formation 187 

lone Formation 187 

"Auriferous gravels" 187 

Lovejoy Formation , — 188 



r- 



CONTENTS-Continoed page 

Oligocene 188 

Wheatland Formation 188 

Reeds Creek Andesite 189 

Ingalls Formation 189 

Miocene 189 

Delleker Formation and its probable equivalents 189 

Bonta Formation 191 

Pliocene 191 

Penman Formation and its probable equivalents 191 

Warner Basalt ., 192 

Plio-Pleistocene lacustrine deposits 192 

Pleistocene and Recent 192 

Glacial deposits „ 192 

Terrace deposits _ 193 

Alluvium 193 

Geologic structure 193 

Petrology 1 95 

References _ 197 

Cenozoi'c yolcanism of the central Sierra Nevada, Califorriia, 

by David B. Slemmons _ _ _ 199 

Resume of the Cenozoic history of the Sierra Nevada 199 

Early rhyolitic activity _. 201 

Earlier andesitic activity _ 203 

Stanislaus Formation . _ 203 

Postlatite volcanic rocks 205 

Petrochemistry _ 207 

References 208 

Economic mineral deposits of the Sierra Nevada, by William B. Clark 209 

Gold 209 

Copper and zinc _ 209 

Chromite, asbestos, nickel, and other deposits in serpentine 209 

Limestone and limestone products 212 

Tungsten _ _ 213 

Barite 21 3 

Sulfur _ 213 

Uranium _ 21 3 

References 214 

CHAPTER V. GREAT VALLEY PROVINCE 215 

Summary of the geology of the Great Valley, by Otto Hackel 217 

Stratigraphy 217 

Pre-Uppermost Jurassic rocks _ 219 

Uppermost Jurassic rocks _ _ 219 

Franciscan Formation 219 

Knoxville Formation 220 

Cretaceous rocks 220 

Lower Cretaceous (Shasta) rocks 220 

Upper Cretaceous (Chico) rocks 222 

Tertiary rocks _ _ 223 

Paleocene rocks 223 

Eocene rocks _ 225 

Lower Eocene rocks 225 

Upper Eocene rocks 227 

Oligocene rocks 230 

Miocene rocks 230 

Lower Miocene rocks „ 230 

Middle Miocene rocks 233 

Upper Miocene rocks 233 

Pliocene rocks 234 

Pleistocene and Recent rocks _ 234 



CONTENTS-Continued page 

Igneous activity .._ 234 

Structure 236 

Economic geology 237 

References _ __ 238 

Hydrogeology and land subsidence. Great Central Valley, California, 

by J. F. Poland and R. E. Evenson 239 

Hydrogeology _ 239 

Geomorphology _ 239 

Geologic units _ 239 

Ground-water occurrence and use __ 241 

Land subsidence 244 

Subsidence of the delta 244 

Near-surface subsidence _.. _ 244 

Subsidence due to water-level lowering 244 

References 247 

Economic mineral deposifs of fhe Greaf Valley, by Earl W. Hart 249 

Petroleum __ 249 

Natural gas 249 

Natural-gas liquids 251 

Carbon dioxide _ __ __ 251 

Gold, silver, and platinum 251 

Sand and gravel ._ _ 251 

Clay __ 251 

Gypsum 252 

Peat __._. __ 252 

Coal _ _ 252 

Pumicite 252 

Stone 252 

Gemstones 252 

Other mineral deposits _ 252 

References 252 

CHAPTER VI. COAST RANGES PROVINCE 253 

Geology of the Coast Ranges of California, by Ben M. Page 255 

Overview 255 

Dual core complexes (pre-latest Cretaceous) _. 255 

Granitic-metamorphic core complex 255 

Metamorphic rocks 257 

Granitic plutons 257 

Cretaceous orogenies . 257 

Franciscan eugeosynciinal core complex 258 

Sandstone . . 258 

Shale and conglomerate 258 

Volcanic rocks 259 

Chert and limestone 259 

Metamorphic rocks 259 

Ultramafic bodies 260 

Structure of Franciscan terranes 260 

Age and stratigraphic limits 260 

Peripheral rocks of late Mesozoic age 260 

Great Valley sequence, flanking the Franciscan core . 262 

Northern port of the Great Valley sequence 262 

Southern port of the Great Valley sequence 262 

Upper Cretaceous cover on granitic-metamorphic core 263 

Overlying blanket: Cenozoic shelf and slope deposits 263 

Paleocene rocks .„ _ 265 

Eocene rocks 265 

Oligocene rocks . 266 

Miocene rocks „ 266 

Mio-Pliocene and Pliocene rocks _- 267 

Plio-Pleistocene deposits 267 



1 



CONTENTS-Continued page 

Major structural boundaries 268 

Sierran-Franciscan boundary 268 

Nacimiento fault zone 268 

Son Andreas fault 269 

Probable early Tertiary thrust faulting 270 

Stony Creek fault 270 

Tesla-Ortigalita fault . 271 

Folded thrust near Cholame Valley 272 

Conclusions regarding early Tertiary thrusting 272 

Late Cenozoic folds and faults 272 

Ordinary folds 272 

General character 272 

Role of core complexes 272 

High-angle reverse faults 273 

Late Cenozoic thrust faults 273 

Franciscan-cored antiforms and diapirs 273 

Franciscan-cored antiforms _ 273 

Piercement structures 274 

Strike-slip faults 274 

Overall crustal deformation _ _ 274 

References _ 275 

Granific and mefamorphic rocks of the Salinian block, California 

Coast Ranges, by Robert R. Compton 277 

Santa Margarita to La Ponza area . 277 

Junipero Serra area _ _ 278 

Northern Santa Lucia Range 283 

Gabilan Range _ 284 

Ben Lomond area _ 285 

Montara Mountain and the Forollon Islands 285 

Bodega Head, Tomales-Inverness Ridge, and Point Reyes 286 

Interpretation 286 

References 287 

Tertiary phosphatic fades of the Coast Ranges, by Paul F. Dickert 289 

General features of distribution 290 

Pre-tertiary phosphatic rocks 290 

Eocene and Oligocene phosphatic fades „ 292 

Lower Miocene phosphatic facies . 293 

The middle Miocene phosphatic facies 294 

Contra Costa Basin _ 294 

Santa Cruz Basin _ 295 

Salinas Basin 295 

Santa Maria Basin 298 

Cuyama Basin _. 298 

Western San Joaquin Basin „ 301 

Summary 302 

Pliocene phosphatic rocks _ 302 

References ._ 304 

Quoternory of the California Coast Ranges, by Mark N. Christensen .... 305 

Stratigraphy _ 305 

Structure 309 

Marine terraces 31 1 

Drainage patterns 311 

Dating the orogeny 313 

References _ 313 

Economic mineral deposits in the Coast Ronges, by Fenelon F. Davis . 315 

Environment of mineral deposits . 318 

Mogmatic segregations of chromite 318 

Epithermal deposits of mercury 318 

Hydrothermal deposits of copper 320 

Mefamorphic deposits of chrysotile asbestos.. 320 

Chemical sedimentary deposits of manganese 320 



CONTENTS-Continued page 

Sedimentary deposits of limestone and dolomite _ 320 

Sedimentary deposits of cloy and sfiale - _ 320 

Sedimentary deposits of diotomite 320 

Sedimentary deposits of sand and gravel 321 

Otfier sedimentary deposits _.. 321 

Petroleum _ 321 

References _ 321 

CHAPTER VII. OFFSHORE AREA 323 

The continental margin of northern and central California, 

by Gene A. Rusnak 325 

Bathymetry _ 325 

Sediments 327 

Bedrock _ 328 

Regional geophysics _ 331 

Conclusion . 334 

References _ 335 

Geologic structure on the continental margin, from subboHom 

profiles, northern and central California, by Joseph R. Curray .... 337 

Shallow structure of the continental margin 337 

Faults 340 

Discussion and conclusions 342 

References 342 

Economic deposits of the California offshore area, 

by Thomas A. Wilson and John L. Merc 343 

Beach and neorshore placer deposits 343 

Petroleum 346 

Tar deposits 347 

Barite deposits _ 347 

Glauconite _ 349 

Phosphorite 349 

Manganese nodules 351 

References 353 

CHAPTER VIM. SAN ANDREAS FAULT 355 

Son Andreas fault in the California Coast Ranges province, 

by Gordon B. Oakeshott.. 357 

Location and extent 357 

History of geological investigations 357 

Earthquake history _ 360 

Geomorphic features _. 362 

Stratigraphy along the fault zone north of the 

Tehachapi Mountains 363 

Franciscan Formation 364 

Granitic rocks and Sur Series __ 365 

Upper Jurassic to Upper Cretaceous shelf-fccies rocks 365 

Tertiary and Quaternary formations .- - 366 

Structural history . 367 

Three great faults 367 

Age of the San Andreas fault — 368 

Nature and amount of displacement 368 

Origin of the fault system 371 

References _ 372 

Evidence for cumulative offset on the San Andreas fault in central 

and northern California, by T. W. Dibblee, Jr 375 

Offsets during Quaternary time — 376 

Displacements of Pliocene formations 378 

Displacements of Miocene formations _ 378 

Displacements of Oligocene and lower Miocene formations 381 

Displacements of Eocene formations _ 381 



CONTENTS-Continued page 

Displacements of Mesozoic formations _ 381 

Other displacements on northern part of San Andreas fault 381 

Conclusion 383 

References 383 

Current and recent movement on the San Andreas fault, 

by Buford K. Meade and James B. Small 385 

Port 1. Horizontal movement, by B. K. Meade 385 

Point Reyes to Petaluma 386 

Vicinity of Hayward _ 386 

Vicinity of Monterey Bay_ 387 

Vicinity of Hollister _ 387 

Salinas River Valley. 387 

San Luis Obispo to Avenal 389 

The 35th Parallel to Cajon Pass 389 

Imperial Valley, vicinity of El Centre 389 

Taft-Mohave area 389 

Cooperative project with Department of Water Resources 389 

Resources 389 

Part 2. Vertical movement, by J. B. Small 390 

References 391 

CHAPTER IX. SUBCRUSTAL STRUCTURE _.. 393 

The gravity field in northern California, 

by Rodger H. Chapman 395 

General features of the gravity field 395 

Coast Ranges province and offshore areas 398 

San Andreas fault _ 399 

Great Valley province 399 

Sierra Nevada and Great Basin provinces 401 

Cascade Mountains and Modoc Plateau provinces. _ 402 

Klamath Mountains province 403 

Summary and conclusions _ 403 

References _... 404 

Magnetic data and regional structure in northern California, 

by Andrew Griscom 407 

Coast Ranges and continental margin „ 407 

Pacific Ocean 407 

Continental shelf. 407 

San Andreas fault _ _ 408 

Franciscan Formation 409 

Great Volley _ _ 410 

Great Valley magnetic anomaly 410 

Magnetic anomaly on the east side of the Great Valley 415 

Sierra Nevada — 415 

Great Basin _ _ 416 

References 41 6 

Crustal structure in northern and central California from 

seismic evidence, by Jerry P. Eaton ._ 419 

Methods 419 

Evidence on crustal structure from near earthquakes 420 

Evidence from explosion seismic refraction profiles 420 

Sierra Nevada profile _ 421 

Coast Range profile 423 

Transverse profiles 423 

Summary . 426 

References 426 



CONTENTS-Continued page 

CHAPTER X. FIELD TRIP GUIDES _ 427 

Point Reyes Peninsula and San Andreas fault zone, 

by Alan J. Galloway 429 

Sketch of geology 429 

History 429 

Oil 431 

Acknowledgmenh 431 

References 431 

Road Log _ 431 

Son Francisco peninsula, by M. G. Bonilla and Julius Schlocker 441 

References 442 

Road Log. 443 

Son Andreas fault from San Francisco to Hollisier, 

by Earl E. Brabb, Marshall E. Maddock, and Robert E. Wallace 453 
References — 453 

Hydrogeology field trip East Bay area and northern 

Santa Clara Valley, by S. N. Davis _. 465 

I ntroducf ion . 465 

References 466 

Road Log ^66 

- Sacramento Valley and northern Coast Ranges, 

by D. O. Emerson and E. I. Rich.. _ 473 

Sketch of geology .- 473 

References : 475 

Road Log . 475 

Yosemite Valley and Sierra Nevada batholith, 

by Dallas L. Peck, Clyde Wahrhaftig, and Lorin D. Clark 487 

Sketch of geology... 487 

References 489 

Road Log..... 491 

Mineralogy of the Laytonville quarry, Mendocino 

County, California, by Charles W. Chesterman 503 

Geology 503 

Metabasalt 503 

Metasedimentary rocks 506 

Metachert 506 

Metashale, metaironstone, and metolimestone _ 506 

Summary — 507 

References 507 



PREFACE 

The Notional Meetings of the Geological Society of America often furnish the impetus required for the assembling of the most recent geological 
informotion available for the region surrounding the host city. The publication of this data provides a background for geologists from other areos 
and permits them to get the most out of field excursions run in connection with the meetings. The value of this short-term use of o geologic summary 
of the region, however, is greatly exceeded by the continuing year-after-year use of the publication by mining and petroleum geologists, regionot 
planners, engineers, faculties and students of universities, and other research geologists, os welt as those who ore seeking only to leorn more about 
the world in which they live. Bulletin 170, The Geology of Sovthern California, edited by R. H. Johns and issued in connection with the Geological 
Society of Americo meeting in Los Angeles in November 1954, has proved to have just such continuing value; in fact, it has recently been reprinted. 
This bulletin on The Geology of Northern California, being issued in connection with the Geological Society of America meeting in San Froncisco 
in November 1966, treats the geology of the other half of the State and doubtless will prove to be equally useful. 

The content and organization of this bulletin is largely that which seemed to be most appropriate after helpful discussions with many geologic 
colleagues. Limitations of both time and money led to restricting the authors to a planned number of pages and to illustrations of page size or 
smaller, but it is likely that in many coses this has resulted in a better product. The selection of authors of articles and leaders for the field trips 
was made with the guidance of an advisory committee consisting of W. R. Dickinson, of Stanford University; G. B. Ookeshott, of the California 
Division of Mines and Geology; P. D. Snavely, of the U.S. Geological Survey; and C. A. Wahrhaftig, of the University of California at Berkeley. For 
most, but not all, topics the geologist selected as the committee's first choice was able to contribute. Numerous other authors and topics also were 
considered, but for practical reasons we felt they would have to be omitted, even though we recognized that their inclusion might hove improved 
the bulletin and mode it more complete. 

Although the controlling factor in the selection of authors was a desire to obtain the most qualified geologist available, regardless of his affiliation, 
the resulting selection involved representatives of universities and colleges. State and Federal organizations, and private industries. Included are 
geologists from the University of California at Berkeley (2), at Davis (2), and at Scripps Institution of Oceanography (1), Son Jose Stote College (2), 
University of Nevada (1), Stanford University (4), University of Southern California (1), University of Hawaii (1), Califorina Academy of Sciences (1), 
California Division of Mines and Geology (8), U.S. Coast and Geodetic Survey (2), U.S. Geological Survey (15), petroleum companies (2), and 
mining companies (2). ^pAi\ 

To the contributing authors, who generally monaged to submit their manuscripts not long ofter their deadline, took my editoriol sniping in good 
grace, promptly and accurately reviewed illustrations and proof, and put forth a real effort to make this bulletin a summary of the Geology of 
Northern California that is scientifically accurate, generally understandable, and a pleasure to read, I offer my sincere appreciation. 

Many people other than the authors also have contributed to this volume, and in the aggregate their contribution in time probably exceeds that 
of the authors. Most of the tedious work of collating, editing, drafting, and some of the proofing was done by the staff at the U.S. Geological Survey 
office in Menio Pork, and the help of this experienced group not only greatly facilitated the preparation of this bulletin but also significantly enhanced 
its quality. Many hundred pages of manuscript were accurately typed and retyped by Frances LeBoker, Mary L. Brannock, Vera P. Campbell, Irene 
Jlminez, and Beatrice L. Sanders. The staff of the Area Publication Unit of the Survey, under the supervision of Henry Berg, aided immensely by 
reviewing articles and references, checking for consistent editorial policy, and proofreading. Particular thanks ore due to Catherine C. Campbell, 
Alice A. Porcel, and Cornello Kline for manuscript reviewing, to SumI W. Sumido for assistance with bibliography, and to Susan McMurroy and 
Wornette Ching for proofreading. Rudolph W. Kopf, of the Geologic Names Review Staff, offered a great deal of technical assistance and helpful 
guidance regarding the usage of geologic names and proper stratigraphic terminology. 

Final copy for many of the illustrations was also made in the Menlo Pork office of the U.S. Geological Survey. We are indebted to Esther T. 
McDermott, most ably assisted by Foye Koonce and Fidelia R. Portillo, for carefully preparing most of the line drawings and maps that so enhance 
this bulletin. We ore equally grateful to Norman Prime and Christopher Utter for fine photocopying of the drafting and many of the photographs. 
Paul Y. W. Ho skillfully retouched some of the photographs and spliced others for panoromos. 

The complete cooperotion of the staff of the California Division of Mines and Geology throughout every stoge in the preparation of this bulletin, 
from its initiol conception to Its final delivery, contributed greatly to its quality. Ion Campbell, State Geologist, actively supported its publication both 
by his own personal interest and by offering the osslstance of members of his staff. Gordon B. Ookeshott and Tom E. Goy deserve special thanks 
for technical aid and odvice, but many others also contributed. Some finished drafting was prepared by Merl Smith and his staff. Final assembly of 
the bulletin and many other editorial matters were adeptly handled by Mary Hill, who also contributed several of the most attractive photographs. 

Students of California geology now have available bulletins on the geology of both southern Colifornla and northern Californio, which will aid 
greatly in understanding the geologic history of the State. Neither of these bulletins, however, provides on entirety satisfying geologic account, 
because neither presents an integrated report describing what events were occurring simultaneously throughout the whole of either area through 
geologic time. This is not the fault of the authors, who hove prepared excellent summary articles on the topics on which they agreed to write; perhaps 
it is a necessary consequence of publication limitations or the need for multiple authorship to cope with the complex and diverse geology In on area 
as large as even half of the State. Regardless of the couse, each bulletin consists chiefly of separate discussions of the geology of smoiler individual 
areas, ranging in size from less than a quadrangle to a province, with little mention of what is beyond thot limited area. But even though geologic 
provinces ore distinct and each tells a different story, what happens in one province— be It erosion, deposition, intrusion, or tectonism— does affect 
bordering provinces. In reaching on understonding of these relations, authoritative province summaries, such as presented here and in Bulletin 170, 
ore a necessary first step, especially now that the literature has become so voluminous and geologists so specialized. With this step accomplished, it 
is hoped thol we can look forward to still broader concepts regarding the interplay of geologic events among the provinces of this State, end to 
early publicotion of a truly integrated geologic history of the entire State of California. 

EDGAR H. BAILEY, Editor 
U.S. Geological Survey 
Menlo Pork, California 



I 



SCOPE AND ARRANGEMENT OF THE BULLETIN 

California is readily divisible into natural provinces, eoch of which has characteristic geography and 
topography, reflecting fundamental differences in geology, see figure 1. The geologic history for each 
province is different from that of its neighbor, and consequently the rocks, structures, mineral deposits, 
ond geomorphology also are different. Six of these provinces— Klamath Mountains, Cascade Range, Modoc 
Plateau, Sierra Nevada, Great Valley, ond Coast Ronges— comprise the area that is generally regarded as 
northern California. In addition, two small parts of the Great Basin province that penetrate into the 
northeastern corner of the state are also included in northern California. The much larger port of the 
Great Basin province that extends in Colifornio north from the Mojave desert to Mono Lake has closer 
geologic affinities, as well as cultural ties, to southern California and is generally considered as a part 
of southern California even though its northern extremity is farther north than Son Francisco. 

Following on historical summary of State geologic maps of California, there is a chapter devoted to each 
of the provinces, or in one case to a group of related provinces, and the leading article for each chapter 
is a summary of the main geologic features of the province prepared by a specialist in that area. Supple- 
menting these summary articles are shorter papers treating some geologic aspect of the province of 
particular interest, either because it is unusual, recently discovered, or of economic importance. 

The area beneath the sea offshore from northern California has attracted considerable interest in recent 
years because of its potential for oil and other mineral resources. It is treated herein in much the some 
manner as the onshore geologic provinces, though it is recognized that the port extending out to the base 
of the continental slope Is in reality just a submerged part of the Coast Ranges province. 

No discussion of the geology of California, especially northern California, con be considered as complete 
without some special treatment of Its best known, and most feared, geologic structure— the great San 
Andreas fault. It is the subject of three articles, two of which present strongly opposed views of the total 
amount of offset along the fault, while the third presents new data that indicate how fast the blocks on 
each side of the fault ore now moving relative to each other. 

The geology at depths below those penetrated by mines or drill holes Is always speculative, being 
either based on downward projections of known geology or on geophysical measurements. The wealth of 
new geophysical data that has become available in recent years provides new insight into deep crustal 
structures, and we can expect much more information will become available soon because of the much 
larger geophysical programs now underway. The information on the crustal structure of northern California 
now available from geophysical measurements— gravity, magnetic, and seismic— Is summarized by articles 
prepared by experts in each of these fields. 

Lastly, a series of roodlogs is Included to aid geologists taking guided field trips that are being run In 
connection with the Notional Meeting in San Francisco of The Geologic Society of America. The logs ore 
all written, however, in such a fashion that they will provide the information necessary for one to observe 
and learn about the geology along the route even on a self-guided tour. 



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Figure 1. Relief map of California showing the naturol pn 



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LISTE. DES tXPLORATtURS GtOLOGiSTtS DE CES REGIONS 

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Geologic mop of California and Nevodo: 
being a portion of Esquisse geologique des 
anciennes possessions mexicaines du nord 
incorporees a lo federation des Etots-Unis. 

Echelle de » rlr. ^^^ ■ ^867. From 

8,000,000 
E. Guillemin-Taroyre, Amission scienfifique 
ou fAex\<:\\ie et dons /'Amerjque cenfro/e 
. . . Poris, }%7y. 



CHAPTER I 
INTRODUCTION 

Poge 

1 Scope and arrangement of the bulletin 

5 State geologic mops of California — a brief history, by Charles W. Jennings 

[3] 







From Codwoloder Ringgold, U.S.N., A seriei of charts, with sailing directions . . . 1852. 



[4] 



STATE GEOLOGIC MAPS OF CALIFORNIA— A BRIEF HISTORY 



By Charles W. Jennings 
California Division of Mines and Geology, San Francisco 



It has been more than 125 years since the first geo- 
logic map of a part of California was published, and 
nearly 100 years have passed since the first geologic 
map of the entire State was prepared. In order to ap- 
preciate more fully our modern geologic maps, it is 
desirable to refer to the earlier maps and compare 
the development and progress through the years. Great 
advances are e.xpected, but often current concepts 
considered as recent developments are found upon 
investigation to have had their seeds sown long ago. 

The history of geologic exploration and mapping 
in California is a colorful and significant one, closely 
associated with the economic and social development 
of the "Golden State." California, early in its history, 
became a training ground for many illustrious pioneers 
in the field of geology. This is not at all surprising, 
considering the wide diversity and complexity of the 
geology and its fabulous mineral wealth. 

The first geologic explorations in California were 
closely associated with the search for gold, and, sec- 
ondly and relatedly, with the surveys for railroad 
routes to the Pacific. After the railroads were built and 
the gold hysteria had lessened, geologic mapping in 
the State proceeded in a more orderly fashion as the 
Federal and State surveys gathered information for 
the continued economic development of the State. Be- 
ginning at the turn of the century, the University of 
California and Stanford University began to make 
important contributions to the understanding of the 
geology of California, especially in basic geologic re- 
search. Later, all of these groups, plus petroleum and 
other mineral exploration companies, pushed the fron- 
tiers of California geologic mapping further back until 
there remain today but few areas for which there ex- 
ists little or no geologic mapping. 

The following discussion of the history of California 
geology focusses on those pioneers who prepared the 
first geologic maps on a statewide scale. No attempt 
has been made to include all those who labored in the 
field in various corners of the State and upon whose 
information the geologic map compilers often had to 
depend. For the history of those stalwart men, whose 
work was often done under conditions of hardship 
impossible to imagine today, the reader should consult 
such references as F. M. Anderson's "Pioneers in the 
geology of California" (1932); George P. Merrill's 
"Contributions to the history of American geology" 
(1906); and V. L. VanderHoof's "History of geologic 
investigation in the Bay region" (1954). 



THE FIRST GEOLOGIC MAPS-1826, 1850 

The honor for the first geologic map of any part of 
California goes to Lieut. Edward Belcher for his "Geo- 
logical plan for the port of San Francisco" prepared 
in 1826 and published in 1839. This map accompanies 
a geologic report by Rev. Buckland (1839) that is in- 
cluded in the volume entitled "The zoology of Captain 
Beechey's voyage" (fig. 1). This is a most remarkable 
geologic and topographic map made with exceptional 
skill. It was surveyed onl\- 17 years after William 
Maclure, "the father of American geology," produced, 
in 1809, the earliest attempt at a geologic map of the 
United States (a map of the region east of the Missis- 
sippi River). 

The first map of a relatively large segment of Cali- 
fornia on which an attempt was made to show the 
distribution of rock types, and the first report that 
attempted to treat the geology of much of the State, 
was prepared by Philip T. Tyson and published by 
the U. S. Government in 1850. This map, entitled 
"Geological reconnaissances in California," accom- 
panied his report "Geology and topography of Cali- 
fornia" which was published as Senate Executive 
Document 47, and privately the following year under 
the title "Geology and industrial resources of Cali- 
fornia." 

The publication of this official report was of great 
importance, for v.'ith the discovery of gold in Cali- 
fornia in 1848 there had arisen an intense demand for 
information on the geology of this practically un- 
known region. Tyson, a private citizen having geo- 
logical training, came to California soon after the 
discovery of gold. Upon his return to Baltimore, he 
offered to Col. J. J. Abert, of the Bureau of Topo- 
graphical Engineers, a copy of the memoir he made 
during his visit west. Abert submitted the report to 
the Senate for publication in compliance with their re- 
quest for any recent reports concerning the geology 
and topography of California. 

Tyson's geologic map included the central part of 
the State and was highly generalized and uncolored, 
perhaps barel>' qualifying as a geologic map. Word 
descriptions lettered on the map were employed in an 
attempt to show the distribution of various rock 
types. It was, nevertheless, the first attempt at a re- 
gional geologic analysis of the State, and together with 
the report and eight cross sections constituted a nota- 
ble effort to describe the geology of California. 



:?] 



Geology of Northern California 



Bull. 190 




Figur. 1. Fir.t geologic mop of an area of Colifornio, .urv.y.d in 1826 by Li.ut. B.lch.r of Hi. Majesty's Ship B/o«om, with the assistance of 
Ship's Surgeon, Alex Collie. This hond-color.d mop of the headland, surrounding Son Francisco Boy depicts five geologic units, including s.rp.nl.ne, 
jasper, claystone, sandstone, and alluvium. 



1966 



Jennings: Gfologic Maps 



Tyson's report was principally concerned with warn- 
ing overadventurous gold seekers and investors, and 
he was quite prophetic when he stated: 

Notwithstanding the seeming brilliancy of the golden prospects, 
the full development of those branches of industry embraced under 
the general head of agriculture, in connexion with the arts by 
which its products are elaborated, is far more important to the 
permanent prosperity of the country than its precious metals can 
ever become. 

MAPS Of THE RAIIROAD EXPLORATIONS 

In 1853 and 1854, in accordance with Acts of Con- 
gress, a number of expeditions were sent out by the 
Secretary of War, Jefferson Davis, to explore routes 
for a railroad from the Mississippi River to the Pacific 
Ocean. These expeditions were under the command of 
army officers, but nearly all included one or more 
geologists or naturalists. The resulting reports com- 
prise the monumental "Pacific Railroad Reports" — 12 
large volumes (sometimes bound as 13 volumes), many 
beautifully illustrated with geologic maps and engrav- 
ings. Volumes V and VII contain most of the reports 
of geological observations made in California — by 
William Blake and Thomas Antisell, respectively. 
Shorter accounts of California geology by Jules Mar- 
cou appear in V^olume III, and by John S. Newberry 
in Volume VI. 

William P. Blake was associated with the Pacific 
Railroad Survey from 1853 until 1856, and during this 
time traversed a very large part of the State. He soon 
became the most extensive writer and accurate ob- 
server of the geology of California. Volume V, con- 
taining Blake's "Geological Report," published in 1857, 
is still thought provoking and very entertaining. It is 
beautifully illustrated with numerous engravings of 
scenic views and natural history. Among the various 
maps of this volume is the first geologic map that 
specifically and exclusively pertains to California. The 
map is highly generalized and many areas are left 
blank for lack of information, the result of the rapid 
nature of the reconnaissance. Nevertheless, utilizing a 
legend of nine units, a broad brush treatment of the 
State shows the following units: Granitic and meta- 
morphic; Erupted granite and syenite; Serpentine, 
trap, greenstone, and porphyry; Basaltic lava; Meta- 
morphic slates; White and crystalline limestone; Ter- 
tiary and Quaternary (Tertiary rocks generally cov- 
ered by Quaternary wash and detritus); Tertiary 
(including the San Francisco Sandstone); and Allu- 
vium. 

The 40-mile-to-the-inch base map, prepared by Lt. 
Williamson, is about as crude as the geologic mapping. 
It shows Lake Tahoe (here called Lake Bonpland)' 
as one of the smallest lakes in the Cahfornia-Nevada 



^According to Gudde (1960), the lake was discovered by Lt. Fremont 
and his skilled German topographer, Charles Preuss. in 1844, and 
first went by the name of "Mountain Lake." Later Fremont named 
it Lake Bonpland in honor of the French botanist who had accom- 
panied Humboldt on his great journey to South America. In 1854 
friends of the Governor of Cahfomia succeeded in naming it Lake 
Bigler in his honor. However, during the Civil War, Bigler was an 
outspoken secessionist, and a movement was started to change the 
name of the lake to its Washoe Indian name, understood to be 
Tahoe — meaning "big water." 



area, whereas actually it is one of the largest. The 
lake is also shown entirely in Nevada (here labeled as 
Utah, as it was then part of the Utah Territory). 
However, the coastline is well surveyed. An interest- 
ing geographical feature located in the cmbayment of 
the coast between San Pedro and San Diego is labeled 
"Earthquake Bay," probably in recognition of the 
shattering earthquake of 1812 during which 40 lives 
were lost at Mission San Juan Capistrano. 

The geology depicted on the base map is colored 
by hand. A comparison with the same map plate in 
other copies of the Railroad Reports shows that the 
coloring was in wide variance, not only in hue, but 
in location from map to map — not an uncommon fail- 
ing of the hand-colored geologic maps published in 
the old reports. 

Blake's larger scale maps of smaller regions in the 
same volume are much more carefully constructed, 
and one in particular, a "Geological map of the vicin- 
ity of San Francisco" (at a scale of about 2% miles- 
to-the-inch) merits a description. On it six lithologic 
units were employed and shown lithographed in color 
— one of the earliest colored maps to be so printed. 
The units include Serpentine, Trap, San Francisco 
Sandstone, Metamorphosed sandstone. Alluvial, and 
Blown sand dunes. Ages are not indicated on the map, 
probably because of the great uncertainty, but some 
speculations are made in the text. The "San Francisco 
Sandstone," the most widespread unit in the area com- 
prising essentially the Jurassic-Cretaceous "Franciscan 
Formation" of today, is considered to be probably 
Tertiary and possibly partly Upper Cretaceous. 

Blake's accounts on California geology are not con- 
fined to the Pacific Railroad Reports, but include 
reports published over many years in various journals 
and government documents. His published contribu- 
tions to California geology total at least seventy. Blake 
deserves grateful recognition for his accurate and 
honest reporting done under circumstances of great 
hardship. 

In 1855, Jules Marcou, a native of France, published 
in French and German scientific journals a colored 
map of the "United States and the British Provinces 
of North America." This map is the first geological 
map of the whole country from the Atlantic to the 
Pacific Oceans, and is the first map showing geology 
for the entire State of California. However, much of 
the geology depicted must have come from some 
psychic source, for at that time large areas of Cali- 
fornia were still totally unexplored. Marcou had been 
the geologist on Lt. Whipple's party of the 1853-54 
Railroad Survey, which started in Arkansas, entered 
California at Needles, and terminated at Los Angeles. 
His observations along this 2,000 mile route, that ap- 
proximately followed the 35th parallel, are represented 
on a geologic strip map and cross section — both re- 
markably well executed and representing some of the 
best geological work found in the volumes of Railroad 



8 



GroLOGY OF Northern California 



Bull. 190 



Reports. Mowcvcr, this would haiill)- have given him 
the infonnation to interpret the geology of the whole 
State! Consequently, Blake (1856) stn)ngl\- criticized 
Alarcou's 18.55 map and had this to sav about the 
California portion: 



Commencing on the Pacific coosi, the peninsula of San Froncisco 
is represented as composed of erupted and metamorphic rocks, 
being colored the some as the Sierra Nevada and Appalachians. 
The rocks of that peninsula, ond on both sides of the Golden Gate, 
ore chiefly sandstone and shale, and the same formation extends 
olong the shores of the Bay to and beyond Son Jos e. Not only 
the extent and position, but the lithologicol characters of these 
rocks ore discussed in a published report (Williamson, R. S., 1855, 
Preliminary geological report on the Pacific Railroad Route, sur- 
veyed by Lieut R. S. Williamson in California: House Doc. 129, 
Woshington, D. C.) which was in the hands of the author of the 
mop previous to its publication. The representation of the granitic 
rocks is not confined to the end of the peninsula, but is continued 
southward to the western shores of the Tulare lokes where the 
formations are chiefly miocene tertiary, the eruptive rocks scarcely 
appearing. 

The promontory called Point Pinos, which forms the headland 
of the Boy of Monterey, is represented as tertiary, while o 
porphyritic granite constitutes the whole point and forms the coast- 
line south to the Boy of San Carlos, ond is probably continuous 
southward to Son Luis Obispo; forming a high and unbroken line 
of coast, all of which is colored tertiary on the map. Casting the 
eye further south, we find the color denoting the eruptive and 
metomorphic rocks again usurping the place which should be 
colored tertiary, at Point Conception, which consists of beds of 
conglomerate and sandstone. 

The broad alluvial tract at the head of the Gulf of Californio- 
the Colorado desert— is mode to extend nearly due north and 
parallel with the Colorado to the Soda Loke (near Boker, ed.). The 
published description of this valley gives its direction as northwest 
and southeast, extending to the foot of Son Bernordine Mountain. 



MAP OF THE COUNTRY WEST OF THE MISSISSIPPI RIVER-1857 

The U. S. -Mexican Boundary- Survey, conducted in 
1855-56, under the direction of Major W. H. Emory, 
was for r!ic primary purpose of "running and marking 
the boundary line under the Trcat\- of Guadalupe 
Hidalgo." It was also commissioned with the task of 
making "an examination of the country contiguous 
to the line to ascertain its practicability for a railroad 
route to the Pacific, as well as collect information in 
reference to tiic agricultural and mineral resources and 
such other subjects as would give a correct knowledge 
of the physical character of the countr\^ and its present 
occupants." Dr. C. C. Parry was the Survey's botanist 
and geologist, Arthur Schott his assistant. 

The results of this survey were published in 1857, 
and were a significant contribution to the understand- 
ing of the geology of .southernmost California. The 
report also included a ver\- interesting hand-colored 
geological map of the Mississippi X'alley and the coun- 
tr\' westward to the Pacific. This map was prepared 
by James Hall of New York, who acted as the Sur- 
vey's geological consultant, and who also reported 
upon the fossils and rocks collected by the Survey. 
Hall's map was published at a scale of 1:6,000,000, and 
includes within its borders California and all of the 



western territories. It is of iiistorical interest because 
it shows how little was definitelv known about the 
geology of the region. The entire Sierra Nevada was 
shown as "Metamorphic," as well as was most of the 
Transxerse and Peninsular Ranges. The bulk of the 
northern Coast Ranges is shown as "Lava and other 
igneous rocks" and an interesting "Desert Quaternary" 
unit is used to siiow areas in the Sacramento \'alle\-, 
the northern coast, and an area along the coast near 
San Diego. .Much of California is shown unmapped 
and tiiat which is shown, is, we now know, mostly 
incorrect. The base map is also very crude — for exam- 
ple, haclunes for the Sierra Nevada are not shown; 
Lake Tahoe (or Lac Bonpland) is missing; San Pedro 
is identified, whereas Los .Angeles is not. It is difficult 
to understand w hy sucii an inferior base map w as used, 
especialK' when a very excellent topographical map 
made l)\' .Major Emory of exactlx' the same territory 
and on the same scale was published in the same 
report! 



FRANCE EXPLORES CALIFORNIA AND NEVADA-1867 

The next geological map of California deserving of 
mention in this chronological description is a remark- 
able one, and possesses a very interesting histor\". This 
map, prepared by Edmond Guillemin-Tarayre in 1867 
and published in Paris in 1871, is but one of 17 beauti- 
ful plates accompanying an obscure volume entitled 
"Description des anciennes possessions .Mexicaines du 
nord, Mission Scientifique au Mexique et dane I'Amc- 
rique Central, Geologic." This publication apparentl\" 
is \'olume 2 of several volumes describing the geo- 
logical, botanical, archeological, zoological, and lin- 
guistic researciics of a French scientific mission to 
Alexico, California, and Nevada. The geology volume 
was the first to be published, and is confined to Cali- 
fornia and Nevada; however, it verv strangel\- was 
left unfinished for the text stops abruptly after 216 
pages, in the middle of a h\phenated word! 

It is interesting to note that this geologic map and 
volume on geology are not listed in the earliest bibli- 
ographies of geologic maps of California. For example, 
they are not mentioned in Marcou's "Catalog of geo- 
logical maps of America" (U.S. Gcol. Survey Bull. No. 
7) published in 1884, or Vodges' "Bibliography relat- 
ing to the geology, paleontology, and mineral re- 
sources of California" (California State Mining Bur. 
Bull. No. 10) published in 1896. Although the U.S. 
Geological Survey's "Geologic literature on North 
America, 1785 to 1918", published in 1923, enters 
Guillemin's publications, and these are consequently 
picked up and relisted by later indexes, nothing could 



Jennings: Geologic Maps 







iiAiTi'. r.\i.i.Foi',>rK 

>'KX'.\]).\ 

I'm .IW l<».v<>lii('<ruln<«Ml Sur>« vl ~lfr, .It lAiil 

' i8t;7 





t/.V./. 


y/jK K.\ri.ii tri 


• rn 


//c. 


»„!>... •*■«/.».«/■.. 


CE3 






EST) 






...1*1 






















' "k»SSE 

C*L,IF0BN1E 



Figure 2. The first color-lithographed geologic mop focusing on California (and port of Nevada), prepared by Edmond Guillemin-Tarayre in 1867. 
This remarkable map, published in Paris as part of the report of a French scientific mission to Mexico and the "ancient Mexican possessions of the 
north", has heretofore remained virtually unknown in American literature. 



10 



Gf.ology of Northern California 



Bull. 190 



be found in the American literature about this geolo- 
gist and this excellent scientific survey.- 

The volume on geology (1871) is organized into 
r\vo sections — the first on Nevada, and the second 
(and unfinished part) on California. Beginning with 
geographical data on these states, succeeding chapters 
treat the geology, mining districts, and metallurgical 
processes, and the volume ends abruptly in a discussion 
of the gold veins of the Sierra Nevada. 

However, it is the plates which are probably of 
greatest interest to us — seven on California, nine on 
Nevada, and one of the southwestern United States. 
The California plates include two hand-colored geo- 
logic maps of parts of California (an area in central 
California, and an area in the southern part of the 
State), a colored lithographic geologic map, and a 
metallurgic map of California and Nevada, and four 
engravings. The engravings illustrate cross sections of 
Sierran gold mines, the New Almaden quicksilver 
mine, and mining equipment used in the recovery of 
gold and quicksilver. 

A notation on the geologic map of California indi- 
cates that it was based on the geologic investigations 
of the Pacific Railroad, the Geological Sun-ey (Cali- 
fornia's Whitney Survey), and the observations of the 
author (fig. 2). The map bears the date 1867. The 
geology is portrayed in a most impressive manner by 
ten geologic units utilizing both color lithography and 
letter symbols, the latter making it easier to correctly 
identify the various units, not always easy to do on 
early geologic maps. All of California is depicted by 
geologic map units, but the southeastern comer of the 
state is cut off by the map border. The base map on 
which the geology is plotted is very good for its time. 
It identifies a large number of towns, rivers, and lakes, 
and indicates the names of the counties but does not 
attempt to show their boundaries. The geologic inter- 
pretation is remarkably good. In most respects this 
geologic map is much more accurate than any of the 
maps presented prior to that time, and was not sur- 
passed by any other geologic map of the State for 
several years following its publication. What a pity 
that such an informative map should have been buried 
for so long in an obscure foreign publication! 

The accompan\ing "metallurgic" (sic) map bears 
the same date, 1867, and is credited as being based on 
the "latest documents." Using a seven-unit legend, it 
portrays the gold-, silver-, copper-, and mercury-bear- 

* From two French publications, one published by Guillemin in 1869, 
"Exploration mini^ralotjique des rcKioncs mexicaines, suiviede notes 
archeologiqucs ct clhnographiques." and the other, his obituar>' by 
P. Rivet (1920), wc learn that Guillemin, a mining engineer, was 
a member of the scientific expedition to Mexico (including California 
and Nevada) from 1864 to 1866. Judging from these dates, and 
recalling the ill-fated French intervention in Mexico with Emperor 
Maximillian during 1863-1867, wc can see the probable relationship 
between the French scientific expedition of which Guillemin was a 
part, and France's interest in the economic aspects of the Mexican 
region. Guillemin started his research in the very active mining dis- 
tricts of California and Nevada, later continuing his work in Mexico. 
His departure from Mexico in 1866 must have Ix-en premature and 

grobably occurred as a result of the existing adverse political climate, 
urely any Frenchman in Mexico at that time must have been con- 
sidered persona non grata. By 1867 the French troops had with- 
drawn, and Maximillian was captured and executed. 



ing belts, the lignite basins, the bituminous shales, and 
mineral springs — a most remarkable attempt to empha- 
size and locate the economic geology of the State at 
such an early date! 

The colored plate entitled "Geological sketch map 
of the metalliferous regions of California," scale 
1:1,000,000, encompasses central California. It is in- 
teresting to note that the te.xt states that this map has 
been constructed from the observations of T\son, 
Trask, various members of the Geological Survey 
(California's Whitney Survey), and from the recon- 
naissance of the French scientific mission. Mr. Rcmond 
of the California Geological Survey was singled out as 
a source of information on the boundaries of the 
Tertiary strata. This map stands in contrast to another 
plate, at the same scale, of southern California (Santa 
Barbara, Los Angeles, and San Diego Counties) which 
is referred to in the title as the "oil region." 

NINTH CENSUS MAP-1872 

In 1872, Charles H. Hitchcock, Professor of Geol- 
og\- at Dartmouth College, with the assistance of 
W. P. Blake, published a colored lithographed geologic 
map of the United States to accompany the Ninth 
U.S. Census report. The part covering California was 
compiled by Blake, based on his personal observations, 
the Pacific Railroad Reports and reports made for rail- 
road corporations, the Whitney Survey reports, Clar- 
ence King's 40th Parallel Reports, and other unnamed 
sources. 

This map was the first of several editions, another 
appearing the same year, and two others in 1874. The 
considerable differences that appear in the various 
editions are described by Hitchcock in his discussion 
of geological maps of the United States published in 
the Transactions of the American Institute of .Mining 
Engineers (1887). 

THE MISSING WHITNEY SURVEY MAP-1873? 

A mystery surrounds the whereabouts of a geologic 
map of California prepared by the State Geologist 
J. D. Whitney in 1873. In his statement of progress of 
the Geological Survey of California during the years 
1872-73, Whitney describes the map as having been 
prepared. This map, reportedly compiled at a scale of 
36 miles to the inch, is referenced in the U.S.G.S. 
"Geologic literature on North America" (Nickles, 
1923), but apparently was never published, and the 
manuscript map has not been found. Several attempts 
by various people to locate this map in the archives of 
the University of California (where the Whitney Sur- 
vey's collections were ordered to be stored by the 
State Legislature) and at Harvard University (where 
Whitney completed much of the writing for the Sur- 
vey's published reports), and elsewhere, have proved 
to be unsuccessful. It is possible that this map rests 
forgotten in a drawer or box, and hopefully, someday, 
someone will recognize this important map and an- 
nounce its discovery. 



1966 



Jennings: Geologic Maps 



n 




^S^-:. 



Photo 1. An 1864 field party of the Whitney Survey. Left to right, J 
William Brewer, party chief; and Clarence Ki 



Gardner, mining engineer; Richard Cotter, packe 
geologist. Courtesy U.S. Geological Survey. 



Ckology of Northern California 



Bull. 190 




Altlioiigii Whimcy's geologic;!! nuip of California 
lias vanished, liis survey was nevertheless a milestone 
in the development of an understanding of the geology 
of the State. It produced a monumental amount of in- 
formation, eventually published in 8 large volumes — 
2 on geolog)', 2 on paleontology, 2 on botany, 1 on 
fossil plants, and 1 on ornithology. In addition, \\ork 
of the Survey resulted in the publication of a number 
of topographic maps, including the classic "Map of 
California and Nevada" (18 miles to the inch), a vol- 
ume on the auriferous gravels of the Sierra Nevada, 
and several guidebooks to Yosemite. The "auriferous 
gravels" report, written b\- \Vhitne>- after his retire- 
ment and the abolishment of the California Geological 
Surve\-. w as published b\- the Museum of Comparative 
Zoolog\- at Harvard in 1880. It contains the only ge- 
ologic maps b\- the California Geological Survey ever 
made public. It is interesting to note, however, that 
in 1877, the famous New York lithographer, Julius 
Bien, sought to have the California Legislature publish 
an atlas of Whitney's topographic and geologic maps, 
but the legislature turned a deaf car to the appeal for 
funds and nothing came of the proposal (Wheat, 1963, 
.333). 

The Whitnev Surve\- faced enormous difficulties — 
both in the field and in the legislative halls of Sacra- 
mento. Although the act of 1860, naming Josiah 
Dwight Whitney as state geologist, directed him 

". . . to make an accurote and complete Geological Survey of the 
State, and to furnish in his Report of the same, proper maps ond 
diagrams thereof, with a full and scientific description of its rocks, 
fossils, soils, and minerals, and of its botanical and zoological 
productions," 

it seems that almost immediately Whitney ran into 
resistance in the legislature and had to spend an enor- 
mous amount of time defending his survey and fight- 
ing for appropriations to continue. The Survey lasted 
from 1860 until 1873. It included on its staff an im- 
pressive arra\- of talent, including such men as Wil- 
liam H. Brewer, Clarence King, Charles Hoffmann, 
William Gabb, James T. Gardner, James G. Cooper, 
and William Ashburner'' (photo 1). 

MARCOU'S MAP OF CAUFORNIA-1883 

Following the Whitney Geological Survey, there 
was published in 1883, a geologic map of California by 
the remarkable and energetic Jules Marcou (fig. 3). 
This map, published in the Bulletin of the Geological 
Society of France, accompanied a report on the geol- 

* Brewer returned to Yale as Professor of Agriculture and played an 
important part in the development of soil science. King, who came 
to Whitney as a volunteer assistant, later organized and directed the 
40th Parallel Survey, and, at the age of 37, became the first Director 
of the U. S. Geological Suricy. Hoffmann may well be called the 
father of modern American topographic surveying having developed 
the methods used by the Federal sur\ey. Gabb. paleontologist of the 
Surx-ey, had helped lay the groundwork for the understanding of 
the Triassic, Cretaceous, and Tertiary of California, before dying at 
the age of 39. Gardner joined King in the Survey of the 40th 
Parallel and later was connected with the Hayden Surveys. Cooper, 
trained as a physician, became noted as a zoologist and paleontologist 
and published a number of papers including several on Cretaceous 
and Fcrtiary fossils. Ashburner, after leaving the Whitney Sun'ey, 
practiced as a mining engineer and became a regent of the Uni- 
versity of California and a trustee of Stanford Ur' 



ogy of California. The map incorporated the interest- 
ing dates 1854—75 in the title; however, it appears that 
these dates do not signify 22 years of work in Cali- 
fornia by the author, hut refer instead to his associa- 
tion with the Pacific Railroad Survey in 1854 and with 
the Wheeler Surve\- West of the 100th Meridian in 
1875. During the intervening _\'ears Marcou was out 
of the State, and for five of those years out of the 
country. 

This page-size map, at a scale of 1:6,000,000, shows 
in colored lithography, nine geologic units for a large 
part of the state. As was typical of most of the geo- 
logic maps of the time, no letter symbols were utilized 
and recognition of the various units on the map is 
often vcr\- tr\ing. One unit (Carboniferous) is diffi- 
cult, if not impossible, to locate on the map. The dis- 
tribution of volcanic rocks in the state is quite good 
for its time. The distrjiiution of the granitic-meta- 
morphic rocks ("Syenite et Roches metamorphiques") 
is fairly good in the Sierra Nevada and Transverse 
Ranges, but quite poor in the southern Coast Ranges. It 
is surprising that Marcou, a paleontologist, recognized 
Cretaceous rocks in only one small area (near Red- 
ding), while Guillemin (1871) recognized the extent 
of Cretaceous strata much more accurately. 

It is interesting to note that the year following 
Marcou's 1883 publication, the U. S. Geological Sur- 
vey, in its 5th Annual Report, published a "Map of 
the United States exhibiting the present status of 
knowledge relating to areal distribution of geologic 
groups" b>- W. J. McGee. This map, surprisingly 
enough, does not show an>- geology for California and 
the other western states, the Survey apparentl\- pre- 
ferring to ignore all earlier maps including .Marcou's. 
This infuriated .Marcou (1892), as indicated by his 
severe criticism of .Mr. McGec, and indeed of the 
entire U. S. Geological Survey from Director Powell 
on down! 

HITCHCOCK'S MAPS OF THE U.S.-1887 

Charles H. Hitchcock again published a geologic 
map of the United States (including a part of Canada), 
which appeared together with his description of geo- 
logical maps of the United States in the Transactions 
of the .\merican Institute of Mining Engineers, 1887. 
This map was based upon the map b\- McGee, but 
most of the parts not colored on that map were filled 
in with data from other sources. Nearly all of Califor- 
nia is colored on the map, with onl\- a small blank area 
in the southeastern part of the state. The general dis- 
tribution of the rocks as we know them today is quite 
good, although it is surprising that the Sierran and 
other granitic rocks are shown as .\rchean (no .Meso- 
zoic granitic rocks recognized in the legend!). The 
map was lithographed b\' Julius Bien of New York, 
and follows the colors adopted by the 3rd Interna- 
tional Geological Congress of 1885. It is a very hand- 
some geologic map and contains surprisingly abundant 
information on the gcolog)' of California. 



1966 



Jennings: Geologic Maps 



13 



N..t. ,i, M MAlJi Ol 



/ \/ l-l l\ I V.,,,., ,l„,l:>.-,lk^.' 




.,; ; I,/.. ,/. : i. 



/«.,. >/.-..,. ,v /;., 



Figure 3. The second color-lithographed geologic mop of Colifornio. Prepored by Jules Morcou following his 
explorations in California in 1854 and 1875, this map was published in the Bulletin of the Geological Society 
of France in 1883. 



14 



Geology of Northern California 



Bull. 190 



FIRST LARGE-SCALE STATEWIDE GEOLOGIC MAP 
OF CALIFORNIA-1891 

In 1880, six years after the Whitney Survey was 
discontinued, the State again felt the need for some 
formal organization to provide information on its min- 
eral wealth; thus the State Mining Bureau was estab- 
lished. Care was taken this time to place at the head 
of the Alining Bureau a "State .Mineralogist," not an 
"academic" geologist or paleontologist, which the leg- 
islature had felt to be so impractical during the pre- 
ceding \VhitneN- Survey! This feeling was so strong 
that not until 1961 was the title of the Chief of the 
State's principal geological organization changed to 
that of State Geologist. 

In 1891, the State Mining Bureau published the 
largest scale geologic map of California prepared to 
that time. This map, on the scale of 1:750,000 (12 
miles to the inch), was entitled "Preliminary miner- 
alogical and geological map of the State of California" 
and was lithographed in color b\' the well-known San 
Francisco firm of Britton and Rcy.^ Beginning with 
this map, the responsibility of preparing and publish- 
ing succeeding editions of large-scale statewide geo- 
logic maps of California has remained with the State. 

The authorship of this geologic map is quite ob- 
scure; the closest approach to a credit line is found 
in the 1 0th Report of the State Mineralogist where on 
page 21 it states: . 

H. I. Willey, ex-Slate Surveyor-General, was engineer in charge of 
the Preliminary Geological and Mineralogical Map, the topograph- 
ical ond other work thereon being executed by Mr. Julius 
Henlienius, who received aid in the geological and mineralogical 
locatings (sic) from the Field Assistants.'* 

On the map itself, the words "Drawn by J. C. Hen- 
kenius" appear in small lettering near the lower edge 
of the map, \\ hile the names of the five members of 
the board of trustees and William Irelan, State Miner- 
alogist, appear in the elaborate title of the map drawn 
in a large hand with numerous flourishes. 

The economic emphasis of this map is quite appar- 
ent, not only in the word "mineralogical" in its title 
but by the choice of certain units in the legend such 
as Auriferous gravels, Auriferous slates, and Lime- 
stone. The locations of known mineral deposits were 
also plotted. 

The geology appears very crude, especially as it is 
plotted on a much larger scale map than ever before 
attempted. However, the general relationship of the 
eight units shown is better than on preceding maps. 
The compiler(s) of this map did not show geology 
for those regions poorly explored and about which 
little was definitely known. The base map used in the 
preparation of this geologic map is noteworthy in that 

• Many of the most important early maps and views of San Francisco and 

California were published by this firm. 

* H. W. Fairbanks, W. A. Goodyear, and W. L. Walts were among the 

"assistants"; thus, very able men contributed to the making of this 
map. 



it was presented as "the first map replete in topogra- 
phy ever made of California." 

In a report on the "Springs of California" published 
by the U.S. Geological Surve>' in 1915, there is a 
"Lithologic map of California" compiled b\- G. A. 
Waring. Though not issued as a state geologic map, 
this small scale map (1:2,000,000), utilizing five carto- 
graphic units, showed the distribution of the principal 
geologic groups throughout the state more completely 
than an\- map to that date. The map notes that the rock 
distribution shown was compiled from published and 
unpublished data of the U.S. Geological Survey, and 
from the 1891 Geologic map of California published 
by the State Mining Bureau. An accompan\ing map 
on the same scale shows the locations of springs and 
faults. The faults arc reported as taken from the atlas 
accompanying the report of the State Earthquake 
Investigation Commission (Lawson and others, 1908), 
This 1908 fault map is probably the first published 
map of the state to show faults. Faults were not de- 
picted on an\' of the earlier described state geologic 
maps, nor on the succeeding geologic map of Cali- 
fornia published in 1916. 

RECONNAISANCE GEOLOGIC MAP OF CALIFORNIA-19)6 

Twenty-five years after the 1891 "Preliminary 
mineralogical and geological map of the State of 
California," the next edition of the geological map was 
published. The preparation of this map had been com- 
missioned by the State Mineralogist, Fletcher Hamil- 
ton, to James Perrin Smith, Professor of Paleontology 
at Stanford Universit^^ This map was published in 
1916, together with a brief bulletin entitled "The geo- 
logic formations of California with reconnaissance 
geologic map" (Bull. 72, Calif. State Alining Bureau). 
This interesting bulletin briefly summarized the geo- 
logic mapping accomplished since the preceding 1891 
map, and described the 1916 map as essentially a report 
of progress. The author states that . . . "he is well 
aware that there are many imperfections. Certain areas 
have not been mapped at all, and others only in a gen- 
eral way." However, an inspection of the map shows 
color and contacts have been applied uniformly to the 
entire area of the State leaving the map user without 
any clue as to what was known and what had been 
projected into the unknown. 

The map legend consisted of 21 geologic units, 
with the Alother Lode and oil fields especially 
delineated — probabl\- in an attempt to give the map 
more of an economic emphasis. The 21 units are 
identified and organized by age and, in addition, the 
Franciscan and Santa Lucia Formations are specifically 
identified. The Franciscan is shown as Jurassic and 
separated from other rocks of Juras.sic age. The Juras- 
sic designation was in contrast to the previously ac- 
cepted Cretaceous assignment by Whitney, Becker. 



1966 



jKNNiNCis: GioLcxiic; Maps 



IS 



and Lawson. This was in keeping with the then cur- 
rent views of H. W. Fairbanks (1898) and the descrip- 
tions of fossils at Slate's Springs in the Santa Lucia 
Mountains by C. H. Davis (1913). Later work clearly 
established the fossils as Late Cretaceous, and as a 
result the strata at Slate's Springs were excluded from 
the Franciscan Formation bv N. L. Taliaferro (1943) 
who assiduously adhered to a Jurassic age assignment 
for the Franciscan. 

The progress portrayed on the 1916 map was largely 
a result of the monumental work done by the U.S. 
Geological Surve\' in the Sierra Nevada, the Coast 
Ranges, and the oil regions. Such illustrious Survey 
geologists as W. H. Turner, Waldemar Lindgren, J. S. 
Diller, and F. L. Ransome became synonymous with 
the Gold Belt studies, and H. W. Fairbanks, Ralph 
Arnold, H. R. Johnson, Robert Anderson, and R. W. 
Pack became the leading authorities on the Coast 
Ranges and oil areas. Additionally, many significant 
contributions were made by Professor A. C. Lawson 
and graduate students at the University of California, 
and bv Professor J. C. Branner and his students at 
Stanford University. 

FAULT MAP OF CALIFORNIA-1923 

Although not a geologic map in the usual sense, it 
would seem appropriate to mention here the relatively 
large-scale (1:500,000) "Fault map of California," pre- 
pared by Bailey Willis and H. O. Wood and published 
by the Seismological Society of America in 1923. This 
map, in the words of Willis, was . . ."designed to 
show the lines on which earthquakes may occur and 
which, therefore, should be avoided by structures 
liable to damage by earthquakes." On it, Willis at- 
tempted to differentiate active faults from "probably 
active faults" and "dead faults". However, the criteria 
used differed significantly in the northern and central 
California map area compiled by Willis, from those 
of the southern California area, compiled by Wood. 
Wood considered as active faults those on which there 
had been some movement within historic time, or 
upon which recent surface dislocation could be found. 
Willis, on the other hand, associated faults with the 
growth of mountains and considered that "any fault 
related to a growing mountain is reasonably subject 
to the suspicion of being an active fault in the sense 
that a slip may occur." Unfortunately, many moun- 
tains in northern California were interpreted on phys- 
iographic evidence alone as being bounded by faults. 
Nevertheless, it remained as the largest scale map of 
the entire State showing faults until the ne.xt geologic 
map of California was published by the State Division 
of Mines in 1938. 

O. p. JENKINS GEOLOGIC MAP OF CALIFORNIA-1938 

The 1 : 500,000-scale geologic map of California, pub- 
lished in 1938, represented 9 years of careful coordi- 
nation of geological research by Olaf P. Jenkins, then 



Chief Geologist of the Division of Mines. Being of 

much larger scale than any previous geologic map of 
the State, considerably more detail was shown, and 
the geologic boundaries were drawn with much 
greater precision, care being taken to follow the source 
data accurately. Unlike many of the earlier maps, blank 
places were left for areas which had not been mapped 
adequately, and little attempt was made at predicting 
or at conjuring what the geology might be. The largest 
blank areas of the map appeared in the northwestern 
part of the State — in the Northern Coast Ranges and 
the Klamath Mountains. Large unmapped areas also 
were left in the southern Sierra Nevada and in the 
desert areas of southeastern California. For the first 
time, faults were depicted together with the areal dis- 
tribution of rocks on a map of the entire State. 

When work on preparing this new geologic map 
of California was started in 1929, the U.S. Geological 
Survey desired to cooperate, since it had undertaken 
the task of making a new geologic map of the United 
States. The Survey prepared a map of California under 
the direction of George W. Stose in Washington, 
D.C., who used data from all available sources, in- 
cluding those gathered by Jenkins in San Francisco 
and sent to Washington. The correlation and adjust- 
ment of the map units of the various authors, and the 
assembling of a comprehensive legend for the State 
map were done by Stose with the cooperation of 
Jenkins at the scale of 1 : 500,000. The resulting Stose- 
Jenkins map, however, was not published on its origi- 
nal scale, but was incorporated in the geologic map 
of the United States, published in 1932, in somewhat 
generalized form for this much smaller scale (1:2,500,- 
000). 

Subsequently, as much new geologic information 
was obtained, new thoughts developed concerning the 
preparation of a 1 : 500,000-scale geologic map, and it 
was decided to completely recompile the map. An 
appropriation was obtained from the Federal Public 
Works Administration, for assisting technical projects 
during the depression period of the 1930's, and from 
this fund came salaries for two additional geologists 
to work on the map under the direction of the Cali- 
fornia Division of Alines. E. Wayne Galliher was as- 
signed the task of compiling the complex geology of 
the Coast Ranges and also contributed some field work. 
Burt Beverly was responsible for most of the photo- 
graphic reduction, the transcribing, and drafting of 
the final map. 

Eighty-one different cartographic units were em- 
ployed on the Jenkins 1938 map. Marine rocks were 
distinguished from continental beds, and the rocks 
were classified into periods of the Paleozoic and Meso- 
zoic, and into periods and epochs of the Cenozoic. In 
addition, the Franciscan and Kno,xville were treated 
separately because so much of the Coast Ranges is 
comprised of rocks of these formations. 



16 



CilOI.tKJY OF NORTHFRN CaLIIOKM A 



Bull. 190 



NEW GEOLOGIC ATLAS OF CALIFORNIA 

The California Division of iMincs and Geology is 
now engaged in preparing and publishing the fourth 
large-scale geologic map of the entire State. This map, 
taking the form of an atlas, will consist of 27 map 
sheets, each at a scale of 1:250,000. One hundred and 
twenty-four cartographic units are being used. The 
preparation of uncolored maps on this scale began in 
1952, and the first sheet, lithographed in color, was 
published in 1958. By late 1965 more than two-thirds 
of the sheets had been printed and were being widely 
used. 

The Geologic Atlas of California presents the re- 
sults of more than 140 \ears of geologic mapping 
in the State, starting from the geologic sketch map 
of San Francisco Ba>' area by Lt. Belcher, prepared 
in 1826. Today, very few completely unmapped areas 
remain, even though several large areas have been 
mapped only in a reconnaissance fashion. We are, 
therefore, just beginning to understand the areal dis- 
tribution of the rock types in California. We know 
even less about the gross structure of the State, 
although we now have a much better understanding 
of the major fault patterns. Nevertheless, much of this 
knowledge has been gained only very recently and 
much still remains to be done. 

Hence, no State geologic map can endure as a final 
and finished product. Each edition essentially repre- 
sents a progress report. At the same time that we care- 
fully map the unexplored or reconnaissanced areas, 
other areas are being studied in greater detail and 
mapped on larger and still larger scales to satisfy spe- 
cial needs. With the increasing wealth of new informa- 
tion, we recognize that our current State map series 
will soon require revision. With this revision in details 
will come a better understanding of the broad geologic 
framework and more accurate answers concerning the 
forces which are responsible for the development of 
geologic structures, as well as some of the answers to 
mysteries of ore deposition and control. Therefore, 
the work of preparing more accurate geologic maps 
has continued and will continue as long as we search 
for a better understanding of the environment in which 
we live. 



REFERENCES 

Anderson, F. M., 1933, Pioneers in the geology of Colifornio, in Shedd, 
Solon, Bibliography of the geology and mineral resources of Colifor- 
nio to December 31, 1930: Colifornio Div. Mines Bull. 104, p. 1-24. 

Blake, W. P., 1856, Review of a portion of the geological mop of the 
United States ond British Provinces by Jules Marcou: Am. Jour. Sci., 
2d ser., v. 22, no. 66, p. 383-388. 

1857, Geologicol report, in Williamson, R. S., Report on exploro- 

tion for railroad route from Mississippi River to Pocific Ocean in 
1853: U.S. Pacific R.R. Explor. (U.S., 33d Cong., 2d sess.. Sen. Ex. 
Doc. 78 ond H. Ex. Doc. 91), v. 5, pt. 2, 310 p. 



Bucklond, W., 1839, Geology, in The zoology of Captain Beechey's 

voyage: London, Henry G. Bohn, p. 157-180. 
Davis, C. H., 1913, New species from the Santo Lucia Mountoins, 

California, with a discussion of the Jurassic age of the slates at 

Slote Springs: Jour. Geology, v. 21, p. 453-458. 
Emory, W. H., 1857, Report on the United States ond Mexican boundary 

survey • • • : U.S. 34th Cong., 1st sess., Sen. Ex. Doc. 108 ond 

H. Ex. Doc. 135, 258, 174 p. 
Fairbanks, H. W., 1898, Geology of a portion of the southern Coost 

Ronges: Jour. Geology, v. 6, no. 6, p. 551-576. 
Gudde, E. G., 1960, California place names; the origin and etymology 

of current geographical names, 2d ed.: California Univ. Press, Berke* 

ley, 383 p. 
Guiilemin-Toroyre, Edmond, 1869, Exploration minerologique des regiones 

mexicoines, suivie de notes orcheologiques et ethnogrophiques: Paris, 

Imprimerie imperiole. 
1871, Description des anciennes possessions mexicoines du nord: 

Paris, France, Mission Sci. ou Mexique et dans I'Amerique Centrale, 

Geologic, pt. 2, 216 p. 
Hitchcock, C. H., 1872, Description of the geologicol mop [of the 

United States]: U.S. Ninth Census, v. 3, p. 754-756. 
1887, The geological mop of the United States ond port of 

Canada 1886, in The geological mop of the United States: Am. Inst. 

Mining Engineers Trans., v. 15, p. 465-488. 
Lawson, A. C, and others, 1908, The California earthquake of April 

18, 1906~report of the State Earthquake Investigation Commission: 

Carnegie Inst. Washington Pub. 87, Atlas, 25 mops and seismogroms. 
Marcou, Jules, 1855, Resume explicotif d'une carte geologique des 

ctats-Unis et des provinces ongloises de I'Amerique du Nord, ovec 

un profil geologique ollant de lo vollee du Mississippi aux cotes 

du Pocifique, et un plonche de fossiles: Soc. Geol. France Bull., 2d 

ser., V. 12, p. 813-936. 
1855, Ueber die Geologische der Vereinigten Stooten und der 

Englischen Provinzen von Nord-Ameriko: Petermonn's Mitt., v. 1, p. 

149-159. 
1883, Note sur lo geologie de lo Colifornie: Soc. Geol. France 

Bull., 3d ser., v. 11, p. 407-435. 
1892, The geological mop of the United States and the United 

States Geologicol Survey; Cambridge, Mass., 56 p. 
Marcou, Jules, and Marcou, J. B., 1884, Mopoteco geologico omericono, 

o catalogue of geological mops of America (North and South), 

1752-1881; U.S. Geol. Survey Bull. 7, 184 p. 
Merrill, G. P., 1906, Contributions to the history of American geology: 

U.S. Notl. Mus. Ann. Rept. 1904, p. 189-733. 
Nickles, J. M., 1923, Geologic literature on North America, 1785-1918: 

U.S. Geol. Survey Bull. 746, 1167 p. 
Rivet, P., 1920, Edmond Guiilemin-Toroyre (necrologie): Jour. Soc. 

Americonistes, n.s., v. 12, p. 236-238. 
Smith, J. P., 1916, The geologic formations of California with recon- 
naissance geologic mop: California State Mining Bur. Bull. 72, 47 p. 
Taliaferro, N. L., 1943, Fronciscon-Knoxville problem: Am. Assoc. 

Petroleum Geologists Bull., v. 27, no. 2, p. 109-219. 
Tysbn, P. T., 1850, * * * information in relation to the geology ond 

topography of California; U.S. 31st Cong., 1st sess.. Sen. Ex. Doc. 47, 

p. 1-74, mop and sections. 
1851, Geology and industrial resources of California: Baltimore, 

Md., 127, 37 p. 
VonderHoof, V. L., 1954, History of geologic investigation in the boy 

region, in Geologic guidebook of the Son Francisco Boy counties: 

California Div. Mines Bull. 154, p. 109-116. 
Vodges, A. W., 1896, A bibliography relating to the geology, paleon- 
tology, and mineral resources of California: Colifornio Mining Bur. 

Bull. 10, 121 p. 
Waring, G. A., 1915, Springs of California: U.S. Geol. Survey Woter- 

Supply Paper 338, 410 p. 
Wheat, C. I., 1963, Mapping the tronsmississippi West: Son Francisco, 

Inst. Hist. Cartogrophy, v. 5, pt. 2. 
Whitney, J. D., 1873, Statement of the progress of the geological 

survey of California during the years 1872-3: [Socromento], 14 p. 
1880, The auriferous grovels of the Sierra Nevodo of California: 

Harvard Coll. Mus. Comp. Zoology, Mem. 6, no. 1, 659 p. 

Willis, Bailey, 1923, A foult mop of California; Seismol. Soc. America 
Bull., V. 13, no. 1, p. 1-12. 



CHAPTER II 
KLAMATH MOUNTAINS PROVINCE 







150 Miles 



Page 
19 Geology of the Klamath Mountains province, by William P. Irwin 
39 Metamorphic geology and granitic history of the Klamath Mountains, by Gregory 

A. Davis 
51 Economic deposits of the Klamath Mountains, by John P. Albers 




[i8] 



GEOLOGY OF THE KLAMATH MOUNTAINS PROVINCE 



By William P. Irwin 
U.S. Geological Survey, Menlo Park, California 



The Klamath Mountains geologic province covers 
an elongate north-trending area of approximately 11,- 
800 square miles in northwestern California and south- 
western Oregon. This article, however, deals chiefly 
with the part that lies in California. The province em- 
braces many individual mountain ranges, among which 
in California are the Trinity, South Fork, Salmon, 
Trinity Alps, Scott, Scott Bar, and Marble Mountains. 
The Siskiyou Mountains occupy a large area on both 
sides of the boundary between California and Oregon. 
Northward from the Siskiyou Mountains the terrane 
becomes increasingly subdued and individual ranges 
less distinct. 

Accordant summit levels and highly dissected old- 
land surfaces are striking features of many of the 
ranges in the Klamath Mountains. The crestlines gen- 
erally reach altitudes between 5,000 and 7,000 feet, 
and locally culminate in peaks as high as 9,000 feet 
above sea level. Features indicating former glaciation 
are seen along many of the crests, but the glaciers 
themselves are now virtually extinct. 

The slopes of most of the ranges are heavily tim- 
bered with fir and pine, particularly in the western 
part of the province. The thick forest cover is due 
largely to a heavy rainfall that occurs mostly during 
the winter months. Most of the rainfall drains west- 
ward to the ocean through deep canyons of the 
Klamath and Trinity Rivers in California and the 
Rogue River and its tributaries in Oregon. The drain- 
age is transverse to the lithic and structural grain of 
the province. The easternmost part of the area in 
California is drained to the south by the Sacramento 
River. 

The Klamath Mountains lie generally between U.S. 
Highway 101 on the west and U.S. 99 on the east, 
except where U.S. 99 diagonally crosses the province 
in Oregon. Roads crossing the province from west to 
east, connecting U.S. 101 to U.S. 99, are U.S. 199 
from Crescent City to Grants Pass, U.S. 299 from 
Areata to Redding, and California Route 36 from near 
Fortuna to Red Bluff. California Route 96 is the prin- 
cipal access to much of the area that lies between U.S. 
199 and U.S. 299. 

The province is thinly populated, the largest towns 
being Roseburg (pop. 11,467) and Grants Pass (pop. 
10,118) in Oregon. Larger centers of population near- 
by include Medford, Ore., and Redding, Calif., on the 
east, and Eureka, Calif., on the west. Settlement of the 

* Publication authorized by the Director, U.S. Geological Survey. 



area began with the discovery of gold in the southern 
part of the province in 1848. Production of gold and 
other metalliferous commodities was the chief indus- 
try until the early 1900's. Lumbering is nov\- the prin- 
cipal industry. 

.Many geologists have contributed to our knowledge 
of the stratigraphy and structure of the Klamath 
Mountains, but space limitations do not allow mention 
of all of them. Of the early work, the contributions of 
J. S. Diller of the U.S. Geological Survey have had the 
most profound and lasting influence. During the late 
1800's and early 1900's, Diller mapped several 30- 
minute quadrangles in Oregon and California, of 
which the most important is perhaps the Redding 
quadrangle. His stratigraphic column of the Redding 
area has well withstood the test of time, having re- 
quired only minor modification in later years. During 
the early 1900's, O. H. Hershey examined mines and 
prospected in the area, and his talent for understand- 
ing regional geologic relations led to important con- 
tributions. Much of the eastern part of the Klamath 
Mountains in California was mapped in reconnaissance 
by geologists of the Southern Pacific Railroad during 
the early 1900's and again in the 1950's. 

Much of the early work, particularly that of Her- 
shey, suffered from the lack of adequate base maps. 
All of the area is now covered by modern topographic 
maps at a scale of 1:62,500. During the 1930's and 
1940's, several 30-minute and 15-minute quadrangles, 
mostly in Oregon, were mapped by the U.S. Geologi- 
cal Survey. This work was done chiefly under the 
direction of F. G. Wells, who was assisted notably 
by P. E. Hotz, G. W. Walker, H. L. James, and F. W. 
Cater, among others. Refinements in the Paleozoic 
and lower Alesozoic part of Diller's stratigraphic 
column were made in the Shasta district near Redding 
by A. R. Kinkel, Jr., W. E. Hall, J. P. Albers, and 
J. F. Robertson of the U.S. Geological Survey during 
the late 1940's and early 1950's. Farther east, the 
Upper Mesozoic part of Diller's stratigraphic column 
was modified by A. F. Sanborn of Stanford Univer- 
sity. Reconnaissance mapping of the hitherto un- 
mapped parts of the Klamath Mountains in California, 
chiefly the western part, was done by W. P. Irwin 
and D. B. Tatlock during the middle 1950's. During 
the late 1950's the work begun by the U.S. Geological 
Survey in the Shasta district was extended to the west 
by Albers in the French Gulch quadrangle, and still 



19] 



20 



GlOLCXJY OK NORTHKRN CaLIIORMA 



Hull. 190 



further west by Irwin in the VVeaverville quadrangle. 
Adjacent arca.s along a belt of mctaniorphic rocks in 
the central Klamath jMountains were studied for Ph.D. 
theses by D. P. Cox and P. W. Lipman of Stanford 
University, and by G. A. Davis, AI. J. Holdaway, and 
\V. D. Romc\- of the University of California at 
Berkeley. Other studies as Ph.D. theses at Stanford 
Univcrsit>- include those by W. P. Pratt and C. K. 
Seyfcrt, Jr., in the central part of the province, and 
b\- .M. C. Blake, Jr., along the southern boundary of 
the province. 



The principal rocks of the Klamath Mountains are 
eugcos\nclinal and plutonic rocks that were involved 
in the Nevadan (Late Jurassic) orogeny. For purpose 
of discussion they are distinguished from younger 
rocks b\' use of the term "subjacent." Rocks younger 
than the Nevadan orogeny surround the Klamath 
Mountains and occur within the province as small 
patches at a few places. The\- were deposited on the 
subjacent rocks with great unconformity, and are re- 
ferred to by use of the term "superjacent." 




1966 



Irwin: Klamath Mountains 



21 



SUBJACENT ROCKS 

The subjacent eugcosynclinal rocks range from 
Ordovician to Late Jurassic (Kinimeridgian) in age. 
Tiiey consist of graywacke sandstones, mudstones, 
greenstones, radiolarian cherts, and rclati\el\' minor 
limestone, as well as metamorphic equi\alents of the 
foregoing rock types and abundant granitic and ultra- 
mafic intrusives. Their pattern of distribution is one 
of concentric, rudely arcuate belts, which from east to 
west are referred to as the eastern Klamath,^ central 
metamorphic, western Paleozoic and Triassic, and 
western Jurassic belts (fig. 2). In all the belts except 
the eastern Klamath, a few outliers of rocks of ad- 
jacent belts are found. The arcuate pattern of lithic 
belts is emphasized by linear bodies of ultramafic rock 
that tend to be concentrated along boundaries between 
the belts. Some bodies of granitic rock also are linear, 
and conform to the arcuate pattern. 

Eastern Klamath Belt 

The gross aspect of the eastern Klamath belt is that 
of an eastward-dipping, essentially homoclinal sequence 
that to the west is deformed and terminated against 
ultramafic rocks. The strata of the belt constitute, in 
the aggregate, a column 40,000 to 50,000 feet thick, 
and represent the time from Ordovician to Jurassic 
(fig. 3). Those of Ordovician and Silurian age are ex- 
posed onh' in an isolated northern part of the belt 
(fig. 2). Probable extensions of the belt, northeast into 
Oregon and southeast toward the Sierra Nevada, are 
concealed by a mantle of superjacent rocks. 

Central Metamorphic Belt 

The central metamorphic belt consists chiefly of the 
Salmon Hornblende Schist and Abrams Mica Schist. - 
Inasmuch as the rocks of the central metamorphic belt 
are described in detail in the next article of this vol- 
ume, only the gross features will be given here. 

The rocks of the central metamorphic belt are gen- 
erally separated from those of the eastern Klamath 
belt by ultramafic rocks, and are in fault contact along 
the western border with rocks of the western Paleo- 
zoic and Triassic belt. Windows in the Salmon expose 
the Stuart Fork Formation (Davis and Lipman, 1962). 
.\ few small outliers of Bragdon Formation of the 
eastern Klamath belt occur within the southern part 
of the metamorphic terrane and are separated from 
the metamorphic rocks either b\- ultramafic rocks or 
by faults. The metamorphic rocks are intruded by 
abundant granitic rocks of Jurassic age. At the south- 
ern end of the belt, the metamorphic rocks are over- 
lain with great unconformit\- by Cretaceous super- 
jacent rocks. 



^ The name "eastern Klamath belt" supersedes the name "eastern Paleo- 
zoic belt" (Irivin, 1960), and refers to all the Paleozoic and sub- 
jacent Mesozoic strata of the Klamath Mountains east of the central 
metamorphic belt. 

' The name Abrams Alica Schist as used herein is restricted to dominantly 
micaceous schists that are coextensive with the Salmon Hornblende 
Schist and that have shared a similar metamorphic and tectonic 
history with the Salmon. It differs from the original Abrams Mica 
Schist of Hershey (1901) by exclusion of rocks named the Stuart 
Fork Formation by Davis and Lipman (1962). 



The age of tiic rocks of the central metamorphic 
belt is problematic. The stratigraphic relations between 
the schists and the rocks of known age in adjacent 
belts arc not known, nor is debris from the meta- 
morphic terrane known to be present in any of the 
other subjacent formations. Isotopic ages ranging from 
270±10 m.\'. to .329±1.3 m.y., obtained on hornblende 
from the Salmon and on muscovite from the Abrams, 
indicate a Carboniferous age of metamorphism, and it 
has been suggested that these schists may be metamor- 
phic equivalents of Carboniferous or older strata of the 
eastern Klamath belt (Lanpherc and Irwin, 1965). 
Metamorphism accompanying the tectonic develop- 
ment of the arcuate belt seems a more likel\' h\- 
pothesis than the uplifting and refolding of an ancient 
metamorphic terrane that existed prior to deposition 
of the oldest strata of the eastern Klamath belt. 

Western Paleozoic and Triassic Belt 

The \\ estern Paleozoic and Triassic belt is a struc- 
turally complex eugcosynclinal terrane. It consists 
mainly of phyllitic detrital rocks, rh\thmically thin- 
bedded radiolarian chert, mafic volcanic rocks, and 
lenses of coarsely cr\'stalline limestone. These rocks 
are abundantly intruded by ultramafic and granitic 
rocks. The interlayered rocks generall\- are metamor- 
phosed to a grade low in the greenschist facies, but 
in some large areas, such as in Scott Bar quadrangle 
(Pratt, 1964), and parts of Condrey .Mountain (P. E. 
Hotz, oral communication, 1965) and Sawyers Bar 
quadrangles (Seyfert, 1964), grades as high as amphib- 
olite facies are attained. A large area of schists in the 
Condrey Mountain and Seiad \"alley quadrangles pre- 
viously were shown (Irwin, 1960) as an outlier of 
the central metamorphic belt, but these schists are 
now thought most likely to be metamorphic equiva- 
lents of rocks of the western Paleozoic and Triassic 
belt (P. E. Hotz, oral communication, 1965) with 
which they are included in figure 12. 

Remarkably few fossil localities are known in the 
western Paleozoic and Triassic belt. Fossils in limestone 
lenses at sparsely .scattered localities were collected 
during the early days of reconnaissance, chiefly by 
Diller. In general, these were considered Devonian 
along the western side of the belt and Carboniferous 
along the eastern side (Diller, 1903b). However, most 
of these fossils were later found to be either of inde- 
terminate age or of an age greatly different from that 
originally assigned (Wells, Hotz, and Cater, 1949; 
iMerriam, 1961; Silberling and Irwin, 1962). Few lo- 
calities of fossils now considered of determinate age 
are known. Several limestone lenses within a few miles 
of the eastern boundary along the southern part of 
the belt contain fusulinids of Late Pennsylvania(?) 
and Earl\' Permian ages (Irwin, 1960, p. 26; 1963). 
An ammonite collected from limestone in the south- 
eastern part of the belt is considered middle or 
Late Permian in age (Miller, Furnish, and Clark, 1957, 



22 



Geology of Northern California 



Bull. 190 




EXPLANAT ION 
SUPERJACENT ROCKS 

CD 

Rocka of Cenoioic ■ge 



Rock* of Lite Juristic 

(Tithonitn) to Late 

Cretaceoua age 

SUBJACENT ROCKS 



Western Juraaaic belt 



ern Ptleoioic and Triattic 
belt 

entral metanorphic belt 



Eaatern Klamath belt 






Granitic rocka 



Itraaiafic rocka, in both 
ubjscent snd superjacent 

ter ranea 

Includti iome gabbroic 

roekt 



10 20 30 «0 MILES 



Btoleiy coaplltd ind aodlfltd 
( roa Strand (I«g2 and I 984), 
It I Is and Pscli (I 861 ). and 
Irwin (I960) 



Figure 2. Geologic map of northwestern California and southwestern Oregon. 



1966 Irwin: Klamath Mountains 

Figure 3. Stratigraphic column of subjacent formations of the eastern Klamath Mountains, California. 



23 



Ag<= 


Formation 


Thickness 
in feet 


General features 


References 




Potem Formation 


1,000 


Argillite and tuffaceous sandstones, with minor beds of conglomerate, pyro- 
clastics, and limestone. Lower beds arc probably Early Jurassic. Upper 
beds are .Middle Jurassic (Bajocian). Upper limit not exposed. Overlain 
by post-Jurassic rocks with great unconformity. 


Diller (1906) 
Sanborn (1960) 


Jurassic 


Bagley Andesite 


700 


.'Vndcsitic flows and pyroclastics. Overlies and intcrfingcrs with lower part 
of Polcm Formation according to Sanborn. 


Diller (1906) 
Sanborn (1953, 1960) 




Arvison Formation of 
Sanborn (1953) 


5.090 


Interbedded volcanic breccia, conglomerate, tuff, and minor andesitic lava 
flows. Fossil fragments in many tuff and sandstone beds. .Ammonites indi- 
cate Early Jurassic (Sinemurian) age. Probably gradational contact with 
Potem Formation. 


Sanborn (I960) 




Modin Formation 


5,500 


Basal member of volcanic conglomerate, breccia, luff, and porphyry, with 
limestone fragments from the Hosselkus. Middle member is massive fossili- 
ferous limestones and calcareous sandstones. Upper member is dark thin- 
bedded argillite with interbedded andesitic pyroclastic rocks. Formation 
considered Jurassic by Diller. Probably unconformable beneath Ar\'ison 
Formation. 


Diller (1906) 
Sanborn (I960) 




Brock Sliale 


400 


Dark massive argillite interlayered with tuff or tuffaceous sandstone. Lxjcally 
fossiliferous. Thought to be Late Triassic (\orian) in age. Probably un- 
conformable with overlying Modin Formation. 


Diller (1906) 
Sanborn (I960) 


Triassic 


Hosselkus Limestone 


0-250 


Thin-bedded to massive light-gray limestone. Fossils indicate Late Triassic 
(Karnian) age. Conformable with underlying Pit Formation and over- 
lying Brock Shale. May be lenticular bodies. 


Sanborn (I960) 

Albers and Robertson (1961) 




Pit Formation 


2,000-4,400 


Predominantly dark shale and siltstone, with abundant lenses of metadacite 
and quartz-keratophyre tuffs. Includes lenses of limestone and lava flows. 
Fossils in limestones, including brachiopods. ammonites, and belemnites, 
indicate Middle and Late Triassic age. Generally overlies, but partly 
intertongues with. Bully Hill Rhyolite. 


Albers and Robertson (1961) 




Bully Hill Rhyolite 


100-2,500 


Lava flows and pyroclastic rocks, with subordinate hypabyssal intrusive 
bodies. Contacts gradational; interbedded with and intrusive into Dekkas 
Andesite below, and interbedded with Pit Formation above. 


Albers and Robertson (1961) 




Dekkas Andesite 


1,000-3,500 


Chiefly fragmental lava and pyroclastic rocks, but includes mudstone and 
tuffaceous sandstone. Interfingers with underlying Nosoni Formation. 
Fossils in tuffaceous beds indicate Permian (Capitan) age, but formation 
probably ranges into Triassic. 


Albers and Robertson (1961) 


Permian 


Nosoni Formation 


0-2,000 


Mudstone and fine-grained tuff, with minor coarse mafic pyroclastic rocks 
and lava. Fusulinids. brachiopods, and bryozoans are common. Formation 
separated from .McCloud Limestone, locally by mafic intrusion and else- 
where by disconformity. 


Albers and Robertson (1961) 




McCloud Limestone 


0-2,500 


Thin-bedded to massive light-gray limestone, with local beds and nodules of 
chert. Abundant corals and fusulinids indicate Wolfcamp and probable 
Leonard (Early Permian) age. Relations to adjacent younger and older 
formations not clear, owing to mafic intrusions along much of the contacts. 


Albers and Robertson (1961) 


Pennsylvanian 


Baird Formation 


3,000-5,000 


Pyroclastic rocks, mudstone, and keratophyre flows in lower part; siliceous 
mudstone, with minor limestone, chert, and tuflf in middle part; and green- 
stone, quartz keratophyre, and mafic pyroclastic rocks and flow breccia in 
upper part. Abundant shallow-water marine fossils from middle part 
indicate Visean age. L'ppermost part contains Early Pennsylvanian 
fusulinids. 


Albers and Robertson (1961) 
Skinner and Wilde (1965) 




Mississippian 


Bragdon Formation 


6,000± 


Interbedded shale and sandstone, with grit and chert-pebble conglomerate 
abundant in upper part. Minor pyroclastic rocks and radiolarian chert. 
Fossils sparse. Essentially conformable with overlying Baird Formation. 
Rests variably on Kennett Formation. Balaklala Rhyolite, or Copley 
Greenstone. 


Diller (1906) 

Kinkel, Hall. Albers (1956) 
Albers and Robertson (I%I) 
Albers (1964) Irwin (1963) 




Kennett Formation 


0-400 


Dark, thin-bedded, siliceous mudstone and tuff. Limestone in upper part. 
Fossils from mudstone and limestone include corals and brachiopods of 
late Middle Devonian age. In places is structurally conformable with 
overlying Bragdon Formation. Rests in Balaklala Rhyolite in some places, 
and on Copley Greenstone in others. Thin or absent in westernmost part 
of belt. 


Kinkel, Hall. Albers (1956) 
Albers and Robertson (1961) 
Albers (1964) 


Devonian 


BalaklaU Rhyolite 


0-3,500 


Light-colored quartz-keratophyre flows and pyroclastics. Conformable with, 
and grades upward into Kennett Formation. Greatly variable thickness. 
Thin or absent in westernmost part of the belt. Nonfossiliferous. Pre- 
sumably Middle Devonian. 


Kinkel, Hall. Albers (1956) 
Albers and Robertson (1961) 
Alber. (1964) 


DevonianC?) 


Copley Greenstone 


3,700+ 


Keratophyric and spilitic pillow lavas and pyroclastic rocks. Intertongues 
with overlying Balaklala Rhyolite. Overlain in some places by Kennett 
Formation, and in others by Bragdon Formation. Nonfossiliferous. 
Probably Middle Devonian. Base not exposed. 


Kinkel, Hall. Albers (1956) 
Albers and Robertson (I96I) 
Albers (1964) 


Silurian 


Gazelle Formation 


2,400+ 


Siliceous graywackes, mudstone, chert -pebble conglomerate, tuff, and lime- 
stone. Limestone contains corals, brachiopods, and trilobites indicative of 
Middle and Late(?) Silurian age. Graptolites in shale indicate latest Early 
or Middle Silurian. Devonian rocks in Grouse Creek area, formerly in- 
cluded in Gazelle (Merriam, 1961) should be excluded (Merriam, oral 
communication, 1965). Fault contacts with Duzel Formation. 


Wells, Walker, Merriam (1959) 
Churkin and Langenheim (I960) 
Churkin (1961, 1%S) 
Merriam (I%I) 


Ordovician(?) 


Duzcl Formation 


1,250+ 


Thinly layered phyllitic graywacke. locally with radiolarian chert and lime- 
stone. Limestone has large coral and brachiopod fauna. Top and bottom 
of formation not known. Locally small overturned folds. Formation in- 
volved in northward-plunging synclinorium, and locally thrust over 
Gazelle Formation. 


Well., Walker. Merriam (1959) 



24 



Geology of Northern California 



Bull. 190 



p. 1062-1063). .\iiiiiionitcs of Late Triassic (Karnian) 
age were founci in liincstonc on the boundary between 
Trinity and Tehama Counties in the extreme southern 
part of the belt (Silberling and Irwin, 1962). Fossils 
suggesting a Sikirian and Devonian age are found at a 
single locality near the center of tiie belt (A'lerriam, 
1961). In Oregon, fossils collected by Diller (1914a), 
in addition to more recent collections, are now con- 
sidered to be of Mesozoic age, probably Late Triassic 
(Wells, Hotz, and Cater, 1949, p. 4). 

Names such as the Blue Chert and Lower Slate 
Series of Hershey (1901, 1906, 1911), the Chanchelulla 
Formation of Hinds (19.32), the Gra\back Forination 
of Maxon (1933), and the Applegate Group of Wells 
and others (1949) have been applied to the aggregate 
assemblage of rocks at several places in the western 
Paleozoic and Triassic terrane. However, meaningful 
subdivision into formations has not been accomplished, 
nor are the stratigraphic relations of the rocks known 
from one area to another. Correlation between rocks 
of the western Paleozoic and Triassic belt and those 
in the more systematic sequence of the eastern Klam- 
ath belt has not been established, except that one might 
broadly correlate the Permian and Triassic limestones 
of the western belt with the McCloud and Hosselkus 
Limestones (fig. 3) of the eastern Klamath belt. 




Photo 1 


. Pillow 


structure 1 


n Copley Greenstone, € 


xposed near the 


outh of 


Deodwc 


od Creek i 


n northeastern Weaver 


ville quadrangle. 



Western Jurassic Belt 

The most westerly lithic belt of the Klamath Moun- 
tains includes the Galice Formation of slaty detrital 
rocks and the schist typical of South Fork Mountain. 
The Galice Formation crops out generally in the east- 



ern part of the belt, and the schists occupy a band 
along the western boundary. When the western Ju- 
rassic belt was originall>' outlined (Irwin, 1960), the 
schist of South Fork iMountain was thought likely to 
be metamorphosed Galice Formation. Later work has 
cast doubt on this relation, as well as on the validity of 
considering the schist of South Fork Mountain to be 
a part of the subjacent terrane. 

The Galice Formation was named by Diller (1907, 
p. 403) for exposures of dark slaty mudstone and sub- 
ordinate sandstone and conglomerate along Galice 
Creek in southwestern Oregon. It was redefined to 
include considerable intercalated volcanic rock (Wells, 
Hotz, and Cater, 1949, p. 4). 

In California the Galice Formation has been studied 
in the Gasquct c]uadrangle adjacent to the Oregon 
border. There, the formation is described (Cater and 
Weils. 1953, p. 86) as consisting of a lower metavol- 
canic unit and an upper metasedimentary unit. The 
lower unit consists mostly of meta-andesite flows and 
breccias and is thought to be at least 7,000 feet thick. 
The metasedimcntar\- unit is chiefly slat\' mudstone 
with interbedded grayw acke. The graywacke is gen- 
erally fine to medium grained and ranges from gra\- to 
green where unweathered. It consists principally of 
angular grains of plagioclase, ijuartz, augitc, horn- 
blende, chlorite, cpidote, micas, fragments of volcanic 
rocks, quartzite, shale, shards of devitrified glass, and 
minor carbonaceous and argillaceous material (Cater 
and Wells, 1953, p. 91). The thickness of the meta- 
sedimentary unit in Gasquet quadrangle is estimated 
to be at least 3,000 feet. Thicknesses as great as 15,000 
feet are reported in Oregon (Wells, Hotz, and Cater, 
1949, p. 7). 

The Galice is the youngest known subjacent forma- 
tion, and generall\- is considered to be correlative 
with the Mariposa Slate of the Sierra Nevada. It con- 
tains the Late Jurassic pelcc\ pod Btichia concentric^ 
(Sowerby) which ranges from late Oxfordian to mid- 
dle Kinimcridgian (lmla\-, 1959, p. 157 and fig. 36). 
None of the formation can be much younger than 
middle Kimmeridgian, as the Galice was deformed 
during the Nevadan orogeny, and as some superjacent 
strata arc as old as latest Jurassic (Tithonian). The age 
of the oldest part of the Galice is obscure, and strati- 
graphic relations between the Galice and older forma- 
tions are not known. Exposures of detrital rocks that 
are largely phyllitic were mapped in reconnaissance 
(Irwin, 1960) southward from the Gas(]uet quadrangle 
for nearly the remaining length of the Klamath .Moun- 
tains. These w ere tcntativcl\' correlated \\ ith the Galice 
Idrmarion on the basis of continuitv of the gross 
lirliolog\, but fossils were not found for establishing a 
correlative age. 

Schist forms a narrow sehage along much of the 
150-mile length of the western and southern boundary 
of the Klaiuath Mountains in California (fig. 4). It 
generally occupies the crest and eastern slope of South 
Fork Mountain, a remarkably long and even-crested 



1966 



Irwin: Klamath Mountains 



25 




Figure 4. Distribution of South Fork Mountain and related schists. 
Southern extension (after Ghent, 1965, and Bloke, 1965) is an area of 
rocks considered at least in part equivalent to schist of South Fork 
Mountain. 

ridge that trends northwest, forming the western 
boundary of the Klamath Mountains for nearly 50 
miles in Trinity and Humboldt Counties. At the south 
end of South Fork Mountain, the schist abruptly 
changes trend and continues more nearly eastward 
along Black Rock and Yolla Bolly Mountains toward 
the Sacramento Valley. In the Coast Ranges west of 
the Klamath Mountains, the schist occurs as a shorter 
parallel band along Redwood Mountain. 

Diller (1903b, p. 343) synonymously referred to the 
schist as the southwestern belt of schists and the South 
Fork Mountain belt of schists. At Weitchpec, near the 
confluence of the Trinity and Klamath Rivers, the 
schist was named the Weitchpec Schists (Hershey, 
1903, p. 357; 1906, p. 63), and in southwestern Blue 



Lake quadrangle, the Kerr Ranch Schist (Ogle and 
Manning, 1950, p. 13). For convenience, Irwin (1960, 
p. 29) informally referred to these schists collectively 
as the South Fork Mountain schist, as they are herein. 
They were included as part of the western Jurassic 
belt of the Klamath Mountains, because they were 
thought to be not onI_\' a part of the subjacent terrane 
but probabl\- a metamorphic equivalent of the Galice 
Formation. 

Although the length of exposure of South Fork 
Mountain schist is impressive, it is onl\' part of a nar- 
row belt of low-grade metamorphic rock that is vir- 
tually 300 miles long. South of Yolla Bolly Mountains, 
semischists and schists follow the boundary between 
the Coast Ranges and Sacramento Valley for more 
than 50 miles. These were described as metamorphosed 
Franciscan(?) rocks of the Coast Ranges (Irwin, 
1960). In southwestern Oregon, the northern e.xten- 
sion of the belt of low-grade metamorphic rocks is the 
Colebrooke Schist, which Diller (1903a, p. 2) consid- 
ered equivalent to the schist of South Fork Mountain. 

The South Fork Mountain schist is typically a well- 
foliated quartz-mica schist, and Iocall\' includes thick 
layers of chlorite-epidote-albite metavolcanic rock. 
Some of the metavolcanic layers contain thin crossite- 
or glaucophane-rich layers. The rocks have been 
folded twice. The first folding appears to be along 
northwest-trending axes, with axial planes dipping to 
the northeast. Superimposed on these are eastward 
trending folds that most commonl\- plunge gently to 
the east. The double folding results in much of the 
schist being complexly contorted and in an intricate 
distribution of outcrops of the metavolcanic rock. 
Study of the schist is greatly hampered b\' dense 
forest cover and abundant debris. 

Similar relations in the Yolla Bolly Mountain por- 
tion of the South Fork Mountain schist belt are de- 
scribed in detail by Blake (1965). Lithologic similarity 
of the South Fork Mountain schist to quartz-mica 
schist and metavolcanic rock of the Colebrooke Schist 
has been observed by Blake and Irwin, as well as by 
others. 

Doubt as to the affiliation of the South Fork .Moun- 
tain schist with the subjacent terrane of the Klamath 
Mountains was first raised by Blake and Ghent (1965), 
who consider the schist to have a closer affinity with 
the post-Nevadan Franciscan rocks of the Coast 
Ranges. Along the south side of the Yolla Bolly .Moun- 
tain, Blake (1965) found an essentiall\' complete gra- 
dation from South Fork Mountain schist to semischist 
and platy gra>'wacke of the belt of metamorpho.sed 
Franciscan rocks of Irwin (1960). Farther south in the 
belt of metamorphosed Franciscan, Ghent (1965) 
found a similar metamorphic gradation, with quartz- 
mica schist and metavolcanic rock similar to that of 
the South Fork and Yolla Bolly Mountains. At both of 
these localities, as well as along South Fork Mountain, 



26 



Geology of Northern California 



Bull. 190 




-ifl^riMtnn<» 



Photo 2. View of the remorlcabl/ uniform summit level along the southern port of South Fork Mountain, looking northeast (left) to southeast (right) 
from Mount Lassie (Signal Peak) in the northern Coast Ranges. The same vantage point wos visited by Diller (1902, p. 18), who considered the long, 
even crest of South Fork Mountain to be one of the best developed portions of the Klamath peneplain. The terrane between South Fo/k Mountain 
and Mount Lassie is chiefly Franciscan rocks. Black Lassie Peak is dominantty graywacke and shale; Red Lassie is mainly greenstone. Much of the 
terrane in the foreground is sharply folded ultramofic rock. North Yolla Bolly Mountain is along the southeasterly extension of the belt of schist of 
South Fork Mountain, toward the Sacramento Valley. Bully Choop Mountain, 45 miles distant in the southeast corner of the Weaverville quadrangle, 
is along the easternmost ultramofic belt of the Klamath Mountains. 



the range in metamorphic grade is comparable to the 
Chlorite 1 through Chlorite 3 subzones defined by 
Turner (1938). The rocks of higher grade are thought 
to overlie those of lower grade, and although the 
transition from one zone to another is essentially gra- 
dational, both Blake (1965) and Ghent (1965, p. 388) 
consider that the rocks of higher metamorphic grade 
have been thrust over tho.sc of lower grade. Fossils 
have not been found in the rocks of higher meta- 
morphic grade typical of the South Fork Mountain 
schist, but in the lower-grade rocks that seem grada- 
tional with the schist, pelecypods of Early Cretaceous 
(Valanginian) age have been found (Irwin, 1960; 
Ghent, 1963; Blake, 1965). 

ultramofic Rocks 

Ultramafic rocks are an abundant component of the 
subjacent terrane, and generally crop out as bodies 
\\hosc linear trends accentuate the arcuate structure 
of the Klamath Alountains (fig. 5). They arc chiefly 
peridotite, but varieties range from pyro.xenite to 
dunite. Generally these rocks arc serpentinized, and 
at many places, principally along their borders, they 
are highly sheared. The ultramafic rocks are widely 
distributed throughout much of the province but are 
significantly absent within the South Fork Mountain 
schist and eastern Klamath terranes. Abundant gab- 
broic rocks are included in areas of ultramafic rock 
shown on figures 2 and 5. They are structurally asso- 
ciated with the ultramafic rock, and not with the 
granitic rocks, but whether they are genetically re- 
lated to the ultramafic rock is not clear. 

The largest ultramafic bod\- separates the eastern 
Klamath terrane from rocks of the central metamor- 
phic belt. Its arcuate western boundary is virtually 
continuous for 100 miles in length, and disappears 



beneath a mantle of superjacent strata at both ends. 
The northeasterly extent beneath the young volcanic 
rocks of the Cascade province is not known, but to 
the southeast the ultramafic body probably continues 
beneath a mantle of Cretaceous and younger super- 
jacent strata of the Great Valley and is perhaps repre- 
sented by a line of discontinuous ultramafic bodies 
along the western front of the Sierra Nevada. In the 
Klamath Mountains this impressive exposure is thought 
to be the eroded lip of an ultramafic sheet whose roots 
lie buried to the east beneath rocks of the eastern 
Klamath belt (Irwin and Lipman, 1962). The broad 
area of ultramafic rock that extends eastward from 
the arcuate exposure, and which generally separates 
Ordovician and Silurian strata from Devonian and 
younger strata of the eastern Klamath belt, is inter- 
preted as a broad arch in the ultramafic sheet from 
which the oncc-overlying strata of the eastern Klamath 
belt are largely eroded. The ultramafic sheet is grossly 
discordant with the layered rocks of the eastern Klam- 
ath belt; in the northern part it is in contact with 
Ordovician and Silurian strata, and in the southern 
part with Devonian and Mississippian strata. This 
sheet is of considerable tectonic significance, as it 
seems most likel\- to have deep roots that perhaps 
connect with the mantle. It is the most easterly ultra- 
mafic rock in the Klamath Mountains, and it separates 
a thick section of Ordovician to Late Jurassic strata on 
the east from metamorphic rocks of Carboniferous or 
older age to the west. 

Although linear bodies of ultramafic rock are nu- 
merous west of the central metamorphic belt, their 
structural relations to the enclosing rocks are not clear 
in most cases. The largest and best known of these 
is the Josephine peridotite body (Wells and others, 



1966 



Irwin: Klamath Mountains 



27 



1949), which crops out over a broad area of northern 
Del Norte County and adjacent parts of Oregon along 
the western border of the province. In southern Del 
Norte County, the Josephine body continues as a nar- 
row linear exposure; farther south, it may be repre- 
sented by numerous discontinuous bodies that follow 
the same general trend along the western border of 
the province in Humboldt and Trinity Counties. The 
Josephine body generally intrudes the Galice Forma- 
tion (Cater and Wells, 1953) but along much of its 
western side it is in fault contact either with Fran- 
ciscan rocks (shown as Dothan Formation by Cater 
and Wells, 1953) or with phyllitic rocks that in re- 
connaisance were tentatively assigned (Irwin, 1960) 
to the Galice Formation. The structure is not clear, 
but some of the relations and topograhpic expression 
of the Josephine body suggest that it too may be a 
sheet. Owing to the uncertainty of the earlier assign- 
ment of both the South Fork Mountain schist and the 



,*>'_ ORE GON 

"•C^." CALIFORNIA 




50 MILES 



Figure 5. Map showing arcuate distribution of ultrcmafic rocks In 
Klamath Mountains of California and Oregon. Ultromafic rocks shown 
OS solid block areas. Mantle of Cenozoic rocks shown as stippled areas. 



phyllitic rock west of the Josephine body to the sub- 
jacent terrane, the Josephine body and its possible 
southern extension may more closely delineate the 
western boundary of the province than heretofore 
considered. 

It is not known with certainty that the ultramafic 
bodies of the subjacent terrane were emplaced during 
a single part of geologic time. Nor is it known whether 
they intruded as many separate bodies, or — taking an 
extreme view — whether they are dislocated parts of 
an essentially single great ultramafic sheet that trans- 
gressed successively younger strata from the eastern 
Klamath to the western Jurassic belt. Most of the 
larger ultramafic bodies of the Klamath Mountains are 
clearly part of the subjacent terrane, as they are cut 
by granitic rocks that are reasonably certain to have 
intruded during the Nevadan orogeny. Notably, the 
easternmost ultramafic sheet is intruded by the Shasta 
Bally batholith and related dikes, and a few inclusions 
of ultramafic rock are found in the batholith. How- 
ever, the earlier limit to the age of this sheet is not 
closely fixed, as the youngest strata known with cer- 
tainty to be cut by the sheet are Mississippian. In 
contrast, emplacement of the Josephine peridotite body 
can be dated closely, as it intrudes the Galice Forma- 
tion (Late Jurassic) and is intruded by Nevadan plu- 
tons (Cater and Wells, 1953). Although evidence for 
closely dating the emplacement of most of the ultra- 
mafic bodies is not at hand, a tentative designation of 
Late Jurassic (Nevadan) is permissive. 

Granitic Rocks 

Granitic plutons and associated dikes are widespread 
in the Klamath Mountains but are not uniformly dis- 
tributed among the several lithic belts. They range 
widely in composition, but quartz diorite predomi- 
nates. Plutons are most abundant in the western Paleo- 
zoic and Triassic belt and are much more sparse in the 
eastern Klamath belt. None is known in the South 
Fork Mountain schist. As the granitic rocks are dis- 
cussed in detail in the next article in this volume, only 
a few of their regional aspects will be given here. 

The apparent scarcity of granitic plutons in the 
eastern Klamath belt may result from the plutons not 
reaching to as high a level through the eastern Klam- 
ath strata as in the belts to the west. Abundant granitic 
plutons are exposed in the broad area of ultramafic 
rock that separates the Ordovician and Silurian from 
younger strata of the eastern Klamath belt but are 
sparse in the adjacent strata. This suggests the possi- 
bility that the ultramafic sheet, which presumably 
extends for some distance beneath the strata of the 
eastern Klamath belt, exerted some control over the 
emplacement of the granitic plutons, and that granitic 
plutons may be concealed beneath much of the Or- 
dovician and younger strata. The Shasta Bally batho- 
lith, the largest pluton in the eastern Klamath belt, is 
eroded only to shallow depth, as indicated by arch- 



28 



Geology of Northern Calieorma 



Bull. 190 



toriniiig flow striictiircs (Albcrs, 1964) and erosional 
remnants of an original cap of the contact metamor- 
phosed Bragdon Formation (Irwin, 1963). Albers and 
Robertson (1961, p. 50) have suggested that several 
smaller stocks arc eminences rising above the general 
level of an intrusive mass that may underlie the entire 
area. Other features that ma\' point to concealed plu- 
tons in the eastern Klamath belt are the important 
base-metal sulfide deposits of the East- and West- 
Shasta districts and abundant gold-bearing quartz veins 
along the Devonian-.Mississippian boundary. 




Photo 3. Metobosolt men t of South Fork Mountain in 

southeastern Pickett Peak quu_: ji-i^L- Open folds plunge gently to 
northeast, away from viewer, and ore of second generation. Mineral 
lineation trends from left to right across trend of open folds. 

The granitic plutons of the Klamath Mountains are 
generally thought to have intruded during the Neva- 
dan (Late Jurassic) orogeny. There is little evidence 
of intrusion earlier than Late Jurassic, and none of 
later intrusion. The \'oungest strata of the subjacent 
terrane, the Galicc Formation of Late Jurassic (Kim- 
meridgian) age, are intruded by granitic rocks, as are 
those of older Mesozoic and Paleozoic ages. The 
superjacent strata, the oldest of which are Late Juras- 
sic (Tithonian), are not intruded. Multiple intrusions 
have been described by Hinds (1932) and Maxson 
(1933), among others, but no field evidence has 
been found to indicate two or more distinct and 
widely spaced periods of granitic intrusion. 

Potassium-argon ages measured on biotite from sev- 
eral plutons in the south-central Klamath Mountains 
range from 127 to 133 m.y. (Curtis and others, 1958; 
Davis, 1963; Lanphere and Irwin, 1965), and an age of 
128 m.\'. was similarly measured on hornblende from 
the Shasta Bally batholith (Lanphere and Irwin, 1965). 
Ages of 141 and 146 m._\-. are reported for biotite 
from a pluton in an outlier of subjacent rocks in south- 
western Oregon (Dott, 1964). All of these are consid- 
ered minimum ages, and at best only appro.ximate the 
age of emplacement of the respective plutons. All are 



permissive of a Late Jurassic age of emplacement. The 
span in age from 127 to 146 docs not necessaril\- indi- 
cate a 19 m.>'. period of intrusive activitw The only 
evidence for plutonic intrusion in the Klamath .Moun- 
tains prior to the Late Jurassic is a potassium-argon 
age of 215 m.\'. measured on hornblende (.Mineral In- 
formation Service, 1965, p. 16) from a small granitic 
stock that intrudes Mississippian strata of the eastern 
Klamath belt. 

There is no field evidence in the Klamath .Mountains 
that granitic plutons intruded during the Cretaceous. 
Nor can the youngest of tiie isotopic dates be used to 
support a Cretaceous age for the plutons based on the 
135-m.y. (Kulp, 1961) or 136-m.y. (Casey, 1964) 
assignment for the age of the Jurassic-Cretaceous 
boundar\-. Isotopic dates obtained on both biotite and 
iiornblende from the Shasta Bally batholith are all 
\()unger than 135 m.y. Nevertheless, the batholith is 
part of a subjacent terrane that is overlain with great 
unconformity b>' a blanket of fossiliferous strata that 
internall\- are essentially conformable and that range 
in age from Late Jurassic (Tithonian) to Late Cre- 
taceous. Of this superjacent blanket, the oldest strata 
that are actualh' seen to lie on the eroded roof of the 
batholith are F.arl\- Cretaceous, hut it is untenable to 
consider that the batholith intruded after deposition 
of the Late Jurassic (Tithonian) strata that onl\' a few 
miles distant to the south are conformable beneath the 
Lower Cretaceous. Granitic cobbles arc uncommon in 
the older superjacent strata, but in the Wilbur Springs 
quadrangle two granitic cobbles were collected from 
near the Jurassic-Cretaceous stratigraphic boundary 
below the Biichia crassicollis zone (E. H. Bailey 
and D. L. Jones, oral communication, 1965). A 
potassium-argon age of 138 m.y. (hornblende) was 
determined for one cobble, and 141 m.y. (biotite) and 
152 m.y. (hornblende) for the other (AL A. Lanphere, 
1965, oral communication). These ages agree within 
analytical uncertainty- \\ ith the ages of Nevadan plu- 
tons in the Klamath Mountains, and suggest that plu- 
tons from w hich these ages are obtained were being 
eroded by the end of the Jurassic. 

The lithic and .structural trends of the south- 
ern Klamath Mountains correspond to those of the 
northern Sierra Nevada; at the north end of the Great 
\'alle\- the continuit\- of Ne\adan and older rocks 
between the two provinces is concealed b\' a \vide area 
of Cretaceous superjacent strata. The superjacent 
strata apparently- are not intruded by granitic plutons. 
Thus, abundant Cretaceous plutons indicated b\' i.so- 
topic age dates in the Sierra Nevada must not follow 
the same lithic and structural trend as the Late Juras- 
sic orogcnic belt of the Klamath Mountains and Sierra 
Nevada and must represent an orogcnic pulse that is 
_\oungcr and distinct from that of the Nevadan orog- 
en>-. 

SUPERJACENT ROCKS 

The oldest rocks exposed unconformably on the 
subjacent terrane of the Klamath Mountains are well- 



1966 



Irwin: Klamath Mountains 



29 



bedded marine sedimentary deposits of Cretaceous age. 
Within the province they are preserved as several 
relatively small erosional remnants. These deposits are 
correlative and doubtless once continuous with a sedi- 
mentary prism of similar strata, the Great Valley se- 
quence (Bailey, Irwin, and Jones, 1965), which laps 
onto the subjacent terrane at the southeast border of 
the Klamath Mountains, and which crops out for sev- 
eral hundred miles to the south along the west side of 
the Great Valley. The erosional remnants in the 
Klamath Mountains, which are restricted to the Cre- 
taceous and are at most about 2,000 feet thick, repre- 
sent the thinning edge of the sedimentary prism that, 
along the Great Valley, ranges from Late Jurassic 
(Tithonian) to Late Cretaceous and attains a thickness 
of approximately 40,000 feet. The entire prism of 
strata of the Great Valley sequence is considered su- 
perjacent with respect to rocks involved in the Neva- 
dan (Late Jurassic) orogeny. 

The Cretaceous of the Klamath Mountains consists 
of mudstone, sandstone, and conglomerate, which 
generally are well bedded and firmly indurated. The 
beds commonly range from a fraction of an inch to a 
few feet in thickness. Some are graded, and at a few 
places sole markings can be seen. The sandstone con- 
sists of poorly sorted angular grains of quartz, feld- 
spar, and lithic fragments. Similar to sandstones of 
much of the Great Valley sequence, some of the feld- 
spar grains are potassium-bearing varieties. Where the 
local stratigraphy is known, conglomerate is most 
abundant in the lower part of the section. The clasts 
are most commonly chert and other resistant fine- 
grained rock. At the Reading Creek locality, a con- 
glomerate bed near the base of the section consists 
almost entirely of fragments of mica schist that must 
have come from the large area of schist now exposed 
nearby. 

Fossils are abundant locall\- in several of the patches 
of Cretaceous strata. They are chiefly pelecypods and 
ammonites of Early Cretaceous (Hauterivian) age 
(Anderson, 1938; Imlay, 1960; D. L. Jones, written 
communication, 1964), but at the Big Bar locality 
Biichia crassicoll'is (Keyserling) of the Valanginian 
Stage of the Early Cretaceous was found (R. W. Im- 
lay, written communication, 1958). Fossils of Late 
Cretaceous age are said to occur at a locality just 
south of Hayfork and at another on the east side of 
Hyampom Valley, but this has not been verified. 

Strata that are correlative with the younger part of 
the Great Valley sequence crop out in a narrow band 
along the northeastern boundary of the Klamath 
Mountains in California and Oregon. These are re- 
ferred to the Hornbrook Formation (Peck, Imlay, and 
Popenoe, 1956) and range from at least as old 
as Cenomanian to late Campanian in age. They consist 
chiefly of bluish-grey siltstone, buff-weathering sand- 
stone, and minor conglomerate that lie unconformably 
on the metamorphic and granitic rocks of the Klamath 



.Mountains. The beds dip northeastward at angles be- 
tween 10° and 30°, and they are believed to con- 
tinue northeastward under the lavas of the Cascade 
Range. 

Tertiary rocks are found at few places within the 
Klamath Mountains, although they are abundant along 
the northern and eastern borders of the province. The 
most important of those within the province in Cali- 
fornia are continental detrital rocks of the Weaver- 
ville Formation, which crop out in only a few small 
areas in the southern part of the province and are 
probably Oligocene in age. A few thin patches of 
marine sedimentary rocks of the Wimer Formation 
of late Miocene age occur on crests of ridges in the 
northwesternmost part of California. 

The Weaverville Formation was named by Hinds 
(1932, p. 115), but had been described in earlier re- 
ports by Diller (1902, 1911, 1914b). It was studied by 
MacGinitie (1937) with particular reference to well- 
preserved fossil plants. The formation was once mined 
for placer gold and for coal, and in the past few 
years has been prospected for phosphate. 

The principal areas of the Weaven'ille Formation 
are in the vicinity of Weaverville and Hayfork, with 
smaller areas at Reading Creek, Hyampom, and Big 
Bar. Small patches of possibly related strata are at 
Corral Bottom, Clark Creek, Buckhorn Creek in 
the northern part of Hyampom quadrangle, and on 
the northwest side of Hoopa \''alley. 

The formation includes beds of sandstone, shale, 
conglomerate, tuff, and lignite that are thought to have 
been deposited on flood plains with widespread 
swampy lakes (MacGinitie, 1937, p. 102). Some may 
be estuarine (Diller, 1902, p. 43). Much of the detritus 
came from nearby highlands, as shown by coarse con- 
glomerate that consists in the Weaverville area almost 
entirely of fragments of Salmon Hornblende Schist 
from the adjacent metamorphic terrane. Carbonaceous 
fragments are found throughout much of the forma- 
tion, and locally, such as at Hyampom, lignite forms 
beds as thick as 16 feet (MacGinitie, 1937, p. 96). At 
the Reading Creek area, the lignite and fine-grained 
sedimentary rocks form the lower parr of the section; 
the upper part is predominantly conglomerate (Irwin, 
1963). There, as at Hyampom, Hayfork, and Big Bar, 
small tonnages of lignitic coal have been mined. Some 
of the tuffaceous shales of the Weaverville Formation 
near Hvampom locally contain as much as 20 percent 
P2O, (Lydon, 1964).' 

Fossil plants found in some of the shale and light- 
colored tuffaceous beds were first considered Miocene 
(Diller, 1902, p. 41-45), and later thought to be chiefly 
Eocene (Hinds, 1932, p. 79, 114-116). However, a 
more thorough study of the flora by MacGinitie 
(1937) suggests an Oligocene age. 

The areas of Weaverville Formation are in many 
places bounded by steep faults. In some areas the for- 
mation rests with angular unconformity on Cretaceous 



?0 



Geology of Northern California 



Bull. 190 



strata and elsewhere on pre-Ncvadan rocks. Typically, 
the Weaverviile is deformed by open folds with limbs 
dipping 5° to 20°, but beds along some major faults 
are steep or nearly vertical. The thickness of the for- 
mation is about 1,900 feet at Reading Creek, probably 
not less than 2,000 feet at Hayfork, and about 1,100 
feet at Hyampom; at Big Bar it is a little less than 500 
feet but neither the top nor the bottom of the section 
is exposed (MacGinitie, 1937). 

Marine sedimentarx- beds of .Miocene age occur as 
small patches on ridge tops near the western boundary 
of the Klamath iMountains in Del Norte County. They 
were named the Wymer Beds by Diller (1902, p. 
32-33), and have since been renamed Wimer Forma- 
tion by Maxson (1933, p. 134; see Wilmarth, 1938, p. 
2347). The formation consists of not more than 150 
feet of nearly horizontal beds of friable shale, sand- 
stone, and conglomerate that weathers yellow and red 
in color (Maxson, 1933, p. 134). Imprints of mollusks 
and plants are abundant locally in the beds, and ac- 
cording to F. H. Knowlton (in Diller, 1902, p. 33) 
and Maxson (1933, p. 135), these fossils indicate that 
the formation is late Miocene in age. 

Gravels that occur only at the same general altitude 
as the Wimer and that fill channels cut into the Wimer 
and older formations in the Gasquet quadrangle are 
described by Cater and Wells (1953, p. 104-105). 
These gravels are poorly sorted and include clay as 
well as boulders. Some of the pebbles and boulders are 
fresh and hard, but others are thoroughly weathered 
and crumble easily. They are thought to have been 
deposited shortly after emergence of the Wimer For- 
mation and to be of late Miocene or early Pliocene 
age. Similar gravels that occur for 2 Vi miles along the 
crest of a high ridge northwest of Hoopa Valley were 
considered by Diller (1902, p. 52-54) to have been 
deposited in an ancient bed of the Klamath River. 

QUATERNARY DEPOSITS 

Alluvial deposits of sand and gravel occur along the 
courses of the major rivers and their tributaries, both 
in the beds of the streams and on terrace remnants of 



earlier levels. The only broad area of valley fill within 
the province is Scott Valley, where alluvial fan de- 
posits attain a probable thickness of 400 feet (Olmsted, 
1956, p. 28-29). In most other valleys of significant 
breadth in the Klamath Mountains, such as Weaver- 
viile, Hayfork, Hyampom, and Hoopa Valleys, Qua- 
ternary alluvium is only a thin, patchy veneer. 

Early interest in the gravel was caused by the dis- 
covery of placer gold at the mouth of Reading Creek 
in 1848, which rapidly led to prospecting and settle- 
ment throughout the entire province. Owing to con- 
tinued economic interest in the gravels, they were 
studied along the upper reaches of the Trinity River 
by Diller (1911 and 1914b). Terraces along the South 
Fork of the Salmon River have been described by 
Hershey (1903) in an attempt to relate them to several 
glacial stages; those along the Smith River are de- 
scribed by Cater and Wells (1953, p. 105-106, 124). 

Some of the terrace deposits are perched as high as 
400 feet above the present streams and are more than 
100 feet thick. Many have been well exposed during 
hydraulic placer-mining operations, with old streamcut 
surfaces on the bedrock being exhumed. At the Union 
Hill mine near Douglas City, the gravels filled an 
ancient loop in Weaver Creek (see Irwin, 1963). Ac- 
cording to Diller (1911, p. 26-27), who e.xamined the 
deposit when the exposures were relatively new, the 
upper 115 feet of the deposit is reddish, poorly strati- 
fied cla>', sand, and gravel, which is underlain by 19 
feet of blue gravels, sand, and clay, with a thin car- 
bonaceous layer at the base. Fossil bones and shells, 
associated with the carbonaceous layer, indicate a 
Pleistocene age. The bones are of mammoths, deer, 
and ground sloths. The shells are similar to those of 
living fresh-water species (Diller, 1911, p. 27). 

Evidence of alpine glaciation is abundant along the 
higher ranges of the Klamath Mountains, but the gla- 
ciers are e.xtinct except for two glacierets covering 
several acres in the Trinity Alps (Sharp, I960, p. 337- 
338). Cirques, bedrock basins, marshy meadows, and 
U-shaped valleys are common features of the landscape 




Photo 4. View looking loulhweit (left) to northwest (right) from Elk Camp in northern Goiquet quadrangle, showing accordant summit levels 
the Klamath peneploin in Del Norte County. Terrane is chiefly ultromofic rock. Loteritic soil on some of the upland surfaces has been prospected for 
nickel. Photo by P. f. Haiz. 



1966 



Irwin: Klamath Mountains 



31 



in the higher parts of nian\- of the mountains (see 
Davis, 1933, p. 215, figs. 19, 20; Hinds, 1952, p. 139- 
142, fig. 100; Irwin, 1960, photo 14). Small lakes asso- 
ciated with these features are generally at altitudes 
above 6,000 feet in the eastern part of the province 
and above 5,000 feet along the boundary between Sis- 
kiyou and Del Norte Counties in the western part. 
Near the south end of South Fork Mountain, cirques 
occur below Chinquapin Butte at an altitude of 5,200 
feet on the east side of the ridge. On the north side of 
North Yolla Boliy Alountain are several small cirque 
lakes, and polished and 'striated surfaces extend do\\n 
to an altitude at least as low as 5,600 feet (Blake, 1965). 
The only modem detailed study of glaciation in the 
Klamath Mountains ^\■as in the Trinity Alps area by 
Sharp (1960). He recognized four glacial episodes, of 
which the three youngest are probably Wisconsin and 
the oldest probably pre-Wisconsin. Some less compel- 
ling evidence suggesting both younger and possibly 
considerably older glaciation also was found. During 
the youngest episode there were at least 30 valley gla- 
ciers in the Trinity Alps area. The glaciers were 
shorter and had a higher terminus in successively 
younger stages. The longest glacier — thought to have 
been about 13.7 miles long — occupied the valley of 
Swift Creek during the pre-Wisconsin episode (Sharp, 
1960, table 6). Associated with the glaciers were nu- 
merous moraines, as well as debris flows that extended 
down the vallevs from the glaciers. 



The arcuate, concentric distribution of the lithic 
belts of subjacent rocks is the most obvious gross struc- 
tural aspect of the Klamath Alountains. The lithic belts 
generally are separated by faults, or by linear ultra- 
mafic bodies or granitic plutons. The strata most com- 
monly dip eastward, and small-scale isoclinal folds with 
eastward-dipping axial planes are reported in all belts. 
For the few areas where major folds are mapped, the 
fold axes are essentially parallel to the arcuate pattern 
of the lithic belts. Some of the major folds are iso- 
clinal with eastward-dipping axial planes. Outliers of 
rocks of adjacent belts are found in all except the 
eastern Klamath belt. The foregoing features are inter- 
preted to result from compressional forces normal to 
the arcuate trend, with westward overriding of low- 
angle thrust plates. This mechanism was operative dur- 
ing at least two major pulses — one pulse in the Klam- 
ath terrane during the Nevadan orogeny and a 
second pulse that delineated the general western 
boundary of the subjacent terrane during a younger 
age, probably Late Cretaceous. A third pulse during 
the Carboniferous may be suggested by the isotopic 
ages of Salmon and Abrams schists. 

Structural relations are shown on the schematic 
cross section (fig. 6). For simplicity, the granitic plu- 
tons are not shown, nor are the many Iiigh-angle faults 
that would complicate portrayal of gross relations be- 
tween lithic units. 



The eastern Klamath belt (fig. 6) is an essentially 
eastward-dipping strarigraphic sequence that to the 
west, in its older part near the ultramafic sheet, is 
highly deformed by folding and faulting. Within the 
sequence, however, an anomalous situation exists along 
the boundary between Baird Formation and McCloud 
Limestone (fig. 6, locality l).The boundary generally 
conforms to the arcuate regional pattern, but as 
pointed out by J. P. Albers (oral communication, 
1965), the Baird and older strata are more highly de- 
formed and intruded by dikes and sills than are the 
younger strata to the east. A faunal hiatus that may 
represent most of Pennsylvanian rime is reported by 
Skinner and Wilde (1965) to occur between the up- 
permost (Early Pennsylvanian) part of the Baird and 
the McCloud (Permian). Although Skinner and Wilde 
report seeing little or no evidence of a physical break, 
much of the boundary is the locus of intrusion of dis- 
continuous bodies of mafic quartz diorite in which 
much of the McCloud is engulfed (Albers and Robert- 
son, 1961). The general scarcity of rocks of Pennsyl- 
vanian age in eugeosynclinal sections of the Pacific 
Coast indicates an interruption of marine deposition 
during much of the Penns\lvanian, and the restricted 
intrusion of mafic quartz diorite along the Baird- 
McCloud boundary suggests a major fault. 

Nearer to the ultramafic sheet along the western 
boundary, the Mississippian and older Paleozoic strata 
of the eastern Klamath belt are folded and highly dis- 
located along steep faults. Here the arcuate regional 
structural trend is not as clearly defined as elsewhere, 
and in the French Gulch quadrangle the local struc- 
ture is dominated by the Shasta Ballv batholith and 
other plutonic intrusives (see Albers, 1964, fig. 5). 
The contact between the Bragdon Formation and 
underl\-ing rocks is of particular interest in the French 
Gulch quadrangle, as it is thought to be a low-angle 
thrust fault over a wide area (fig. 6, locality 2), with 
neither the direction nor amount of displacement 
known (Albers, 1964, p. 62-63). 

.'Xlong much of the western boundary of the eastern 
Klamath belt, the ultramafic sheet and adjacent rocks 
are folded into an antiformal structure. The axes of 
the antiform and other major folds in the central meta- 
morphic belt are generally parallel to the arcuate 
trend of the belt along its entire length. 

In Weaverville quadrangle (Ir\vin, 1963), the Brag- 
don Formation and Copley Greenstone wrap over the 
crest of the antiformal fold, and the Copley is pro- 
gressively cut out toward the west by the ultramafic 
sheet (fig. 6, locality 3). Near the laritude where the 
andformal fold is crossed by the Trinity River, the 
Bragdon is separated from underlying schist of the 
central metamorphic belt in the breached core of the 
fold only by the ultramafic sheet, which here is less 
than 200 feet thick and nearly horizontal. The struc- 
tural horizon represented by the ultramafic sheet and 
the overlying Bragdon Formation occurs to the west 
only as two outliers within the confines of the central 




\ q! 01 Hi! 0! 0! I 



» 6 



[3a] 



1966 



Irwin: Klamath Moumains 



33 



metamorphic belt, one in Weaverville quadrangle 
(fig. 6, locality 4) and a smaller one at the south end 
of the belt at the Cretaceous overlap. As described 
earlier in this paper and elsewhere (Irwin and Lipman, 
1962; Irwin, 1964), the ultramafic sheet is thought to 
have intruded a regional fault along which the rocks 
of the eastern Klamath belt are thrust westward over 
rocks of the central metamorphic belt. 

In the Trinity Alps, north of Weaverville quad- 
rangle, the rocks in the eastern part of the metamor- 
phic belt are described (Davis and Lipman, 1962; 
Davis, 1964) as isoclinally folded into a north-trending 
antifornial structure that is steeply overturned to the 
west. The rocks that underlie the Salmon Hornblende 
Schist in the breached core of the fold (fig. 6, locality 
5) are of anomalously low metamorphic grade, and 
are thought to be correlative with rocks of the west- 
ern Paleozoic and Triassic belt. The contact between 
the rocks of the core and the overlying Salmon Horn- 
blende Schist is considered a folded thrust fault along 
which the rocks of the central metamorphic belt are 
displaced a minimum of 15 miles across rocks of the 
western Paleozoic and Triassic belt (Davis, 1965). 
Farther north along the metamorphic belt, in the areas 
studied by Holdaway (1962) and Romey (1962), the 
dominant fold structures continue parallel to the trend 
of the belt except where the\- are deflected by intru- 
sions of granitic plutons. 

The western boundary of the metamorphic belt was 
thought by Hershey (1906, p. 58) to be a regional 
fault along which the schists were thrust westward 
over rocks of the western Paleozoic and Triassic belt, 
and this general idea (fig. 6, locality 6) is substantiated 
to some extent by more recent work of others. In 
Helena quadrangle the boundary is a thrust fault that 
dips 40° to 50° to the east, and, where well exposed, 
Salmon Hornblende Schist on the hanging wall is sep- 
arated from rocks of the western Paleozoic and Trias- 
sic belt by a shear zone a few inches in width (Cox, 
1956, p. 103). To the north in Cecilville quadrangle, 
G. A. Davis (written communication, 1963) also re- 
ports that the boundary is a thrust fault, and that the 
Salmon is thrust over rocks of the western Paleozoic 
and Triassic belt. To the south in Weaverville quad- 
rangle, east-dipping shear planes and phyllonite zones 
that suggest thrusting are locally abundant near the 
boundary, but much of what may earlier have been a 
thrust boundary is perhaps modified by high-angle 
normal faults. Relations along the northern part of the 
metamorphic belt (Holdaway, 1962) also suggest a 
thrust fault. However, the general boundary would 
indeed seem to be fundamentally the lip of a 
thrust if, as suggested by Davis and Lipman (1962), 
the rocks of anomalously low metamorphic grade 
(Stuart Fork Formation) in the core of a major anti- 
formal fold are in thrust contact with overlying Sal- 
mon Hornblende Schist and are correlative with rocks 
of the western Paleozoic and Triassic belt. 



The regional structure of the western Paleozoic and 
Triassic belt is little known but obviously complex. 
The belt has been mapped in detail at only a few 
places, and even at those places an understanding of 
the structure has been hindered by a lack of adequate 
stratigraphic data. However, the trends of certain 
linear lithic units, particularly belts of discontinuous 
limestone lenses (Diller, 1903b; Irwin, 1960, p. 2 3), 
are parallel to the belt, and indicate that the regional 
structural axis also is parallel. Axes of numerous minor 
folds in Permian strata west of the metamorphic rocks 
in Weaverville quadrangle generally trend northwest 
and are subhorizontal. In western Helena quadrangle, 
the strata trend north to northwest, generally dip east- 
ward, and have abundant small folds whose axes strike 
north to northwest (Cox, 1956, p. 98). In Sawyers Bar 
quadrangle to the north, the strata are described by 
Seyfert (1964) as isoclinally folded, with axial planes 
dipping steepl\' east and fold axes plunging gently 
south. Here the folds range from several feet to sev- 
eral thousand feet across and are remarkably continu- 
ous along their trend. 

The western boundar\- of the western Paleozoic 
and Triassic belt was early recognized as a major 
structural break, which in northern Humboldt County 
and northward in California was called the Orleans 
fault by Hershey (1906). During reconnaissance (Ir- 
win, 1960), the rocks of the belt seemed virtually 
everywhere to be separated from younger rocks to 
the west either by ultramafic and granitic rocks or 
by faults. Although Hershey 's Orleans fault corre- 
sponds to some extent to the western boundary of the 
western Paleozoic and Triassic belt, some parts of the 
trace of the fault as dra\\'n by Hershey (1911) differ 
markedly from the boundary of the belt as drawn 
later (Irwin, 1960, pi. 1). Hershey stated that the 
Orleans fault dipped steeply east, and although he 
referred to the Orleans fault as a thrust fault, it was 
clearly in the sense of a high-angle reverse fault. 

There is little positive evidence to refute Hershey's 
concept of an overall high-angle character of the fault- 
ing along much of the western boundary of the belt. 
At some localities, however, the fault is seen to dip 
gently eastward (fig. 6, locality 7). One of these is 
on a major spur ridge east of Hoopa. There the bound- 
ary is marked by a serpentine mass that is laced by 
abundant shear planes that dip gently eastward and 
that includes lenses of rodingite parallel to the shear 
planes. In addition to local suggestions of a gentle 
easterly dip of the fault boundary, several outliers of 
rocks similar to the rocks of the western Paleozoic 
and Triassic belt lie west of the boundary. Linear 
exposures of ultramafic rock form boundaries of some 
of these outliers, and owing in part to the structural 
significance attributed to ultramafic bodies in the 
Klamath Mountains and Coast Ranges (Irwin, 1964), 
these outliers are postulated to be klippen detached 
from a thrust plate of western Paleozoic and Triassic 



34 



Geology of Northern California 



Bull. 190 



rocks that overrode rocks of the western Jurassic belt. 
The western boundary of the western Paleozoic and 
Triassic belt, although now periiaps marked by steep 
faults along much of its length, may fundamentally be 
the upturned edge of a low-angle thrust plate that 
once Axas continuous with outliers to the west. 

The most obvious structure of sedimentary rocks 
of the \\estcrn Jurassic belt is a slaty cleavage that 
commonly dips toward the eastern boundary (fig. 6, 
locality 8). The Galice Formation in Gasquet quad- 
rangle (Cater and Wells, 1953) is deformed by north- 
to northeast-trending folds, parallel to the gross struc- 
tural axis of the province, that are steeply overturned 
to the west. These are associated with high-angle re- 
verse faults that are parallel to the a.xial planes of the 
folds. Faults with other trends postdate the folds and 
reverse faults but are thought to belong to the same 
(Nevadan) period of deformation. South of Gasquet 
quadrangle, the rocks tentatively assigned to the Galice 
Formation appear more phyllitic than to the north, 
and although the bedding and cleavage is commonly 
parallel to the long axis of the belt, the area has not 
been studied sufficiently for the structure to be known. 



The problematic South Fork Mountain schist (fig. 
6, locality 9) forms the western boundary of much 
of the Galice(?) Formation in California. The prin- 
cipal structural axis is essentially parallel to the trend 
of the belt, as shown by northwest-trending isoclinal 
primar)' folds that are overturned to the west. The 
primary folds are modified by secondary- folds whose 
axes trend eastward. Metamorphism of the parent rock 
occurred during the primary folding. Regardless of 
whether the schist formed from Galice Formation or 
from Franciscan rocks, the general structural pattern 
resembles that of the lithic belts to the east and prob- 
ably resulted from similar although perhaps \ounger 
(Late Cretaceous?) directed crustal stresses. Outliers 
of the schist that occur to the west along Redwood 
Mountain (fig. 6, locality 10) and in southwestern Or- 
egon (Colebrooke Schist) are most readily explained 
as klippen (Irwin, 1964). 

The inferred pre-Tertiary thrust structures are 
shown schematically in plan on figure 7. The lithic 
belts of the Klamath Mountains are considered thrust 
plates that successsively overlap adjacent plates to the 
west. Isolated patches of rocks correlative with a spe- 




Pholo 5. View to northeast across McCloud River Arm of Shasta lake. Large oreo of light colored outcrop is McCloud Limestone, separated from 
underlying Baird Formation (darker slopes near lake) by band of intrusive mafic quartz diorite. Approximate position of intrusive contact between 
McCloud ond quartz diorite is shown by black line. Beds in McCloud Limestone strike northwest across northeosterly trace of intrusive contact. Dark 
peck in right background is Horse Mountain, which consists of Dekkas Andesite. Photo by J. P. Albert. 



1966 



Irwin: Klamath Mountains 



35 




30 40 MILES 



EXPLANATION 

Cenoioic rocks 



Upper Cretaceoua 
she If deposits 



Uppermost Jurassic sod 
Lower Cretaceous shelf 
deposits. Not shown on 
outlier of western Ju> 
rassic plate in Oregon 



Eastern Klamath plate 
Central metaoorphic plate 



Western Paleoioic and 
Triassic plate 



Western Jurassic plate 



Uppermost Jurassic and 
Cretaceous plate 



Thrust fault 
Sawteeth on upper plate 



Figure 7. Principal postulated thrust plates of the Klamath Mountains and adjacent Coast Ranges. Thrust outliers are 
indicated by letter symbol: A, Oregon Mountain; B, Willow Creek; C, Prospect Hill; D, Flint Volley; E, Redwood Mountain; 
F, Patricks Point; and G, southwestern Oregon. 



cific belt are interpreted to be thrust outliers (klippen) 
or windows of the plate to which the correlative rocks 
have been assigned. The granitic and ultramafic rocks 
are not outlined on the sketch, and are included arbi- 
trarily with individual thrust plates. Although ultra- 
mafic rock intruded between certain of the thrust 
plates, its inclusion with individual plates does not in 
most cases seriously distort the outlines of the thrust 
plates shown on figure 7. An exception is the outline 



of the eastern Klamath plate, which here includes the 
erosional lip and exposed crest of the broad arch in the 
ultramafic sheet. Thus the eastern Klamath plate as 
shown on figure 7 suggests a reconstruction of the 
strata that formerly bridged the broad arch of ultra- 
mafic rocks. Because of this, the position of the Gray 
Rocks outlier, which forms part of this bridge, is 
shown only by a symbol. 



36 



Geology ok Northern Caliiorma 



Bull. 190 



The central inctamorphic plate lies below the east- 
ern Klamath plate and above the western Paleozoic 
and Triassic plate. The Oregon .Mountain outlier 
(Bragdon Formation) of the eastern Klamath plate 
rests on the central iiietamorphic plate, and, as sug- 
gested by Davis and Lipman (1962), \\'indo\vs at sev- 
eral places along the central inctamorphic plate expose 
portions (Stuart Fork Formation) of the underhing 
western Paleozoic and Triassic plate. Along its western 
border the \\cstcrn Paleozoic and Triassic plate lies 
on the \\cstcrn Jurassic plate, with the Willow Creek, 
Prospect Hill, and Flint Valle\- outliers of the western 
Paleozoic and Triassic plate presumablx' resting on the 
western Jurassic plate. 

These thrust plates are depositionallx' overlapped at 
the south end of the Klamath .Mountains b\' the prism 
of superjacent shelf deposits of the Great \^alley, and 
thus are older than Late Jurassic (Yithonian) in age. 
Whether all the.se thrust plates were developed during 
a single brief orogenic episode is not clear. However, 
if all the relevant ultramafic rocks were emplaced 
during a single brief span of time in the Late Jurassic, 
between the middle Kimmeridgian and Tithonian 
Stages, a similar age span seems likel\' for the major 
thrusting. The thrusting, the emplacement of the 
Klamath ultramafic sheets, and the intrusion of gra- 
nitic batholiths are tentatively considered closely timed 
sequential events of the Nevadan orogeny. 

The South Fork Alountain and related schists are 
included with the western Jurassic plate as shown on 
figure 7, although rather than actually being part of 
the subjacent terrane, they may have formed from 
post-Nevadan (Franciscan) rocks through tectonic 
overpressure along the sole of a thrust. Owing to the 
thinness of this schistose rind, the gross structural 
picture is not greatly affected by whether the rind is 
directly above or directl\' below the thrust. In either 
case, the distribution and other features of the schist 
are mostly readily explained by the subjacent terrane 
being thrust westward over post-Ncvadan (Fran- 
ciscan) rocks of the Coast Ranges along the general 
western boundar\' of the Klamath Mountains. The 
Redwood Mountain and Patrick Point outliers of schist 
in California and the outlier including the Colebrooke 
Schist and other subjacent rocks in southwestern 
Oregon are shown as klippen of the western Jurassic 
plate. 

The post-Nevadan eugeosynclinal (Franciscan) rocks 
along the west side of South Fork Alountain contain 
Earl>- Cretaceous fossils. Even excluding the possibility 
of the South Fork Mountain schist being formed from 
these rocks, the\- are metamorphosed at least to the 
Chlorite 2 subzone in a narrow belt alongside the 
schist. It is noteworthy that in the Klamath Mountains 
only a few miles to the east of these metamorphosed 
post-Nevadan rocks, patches of Cretaceous strata of 
equivalent age but of a shelf facies lie depositionally 
on thrust plates of pre-Nevadan rocks. The metamor- 
phism indicates that the thrusting along the western 



boundary- of the Klamath Mountains was later than 
I'arh- Cretaceous, and the abrupt change in facies of 
Farly Cretaceous rocks across the province boundary 
suggests great horizontal translation along the thrust. 

The thrust along the western boundary of the Klam- 
ath Mountains seems essentially continuous with the 
thrust fault along the west side of the Sacramento 
\^alle>', along which shelf deposits of the Great Valley 
sequence arc thrust westward over eugeosynclinal 
Franciscan rocks with a horizontal translation of 50 
miles or more (Irwin, 1964, p. 6-7; Bailey, Irwin, and 
Jones, 1964, p. 163-165). By analog)-, horizontal trans- 
lation of a similar order of magnitude is postulated 
for thrusting along the western boundary of the Klam- 
ath Mountains. Although the thrusting in both cases 
clearly was later than Earl\- Cretaceous, a post-early 
Late Cretaceous age is suggested by a juxtaposition of 
superjacent shelf deposits of Late Jurassic and Earl\- 
Cretaceous age against eugeosynclinal deposits of 
earl\' Late Cretaceous age in the San Francisco Bay 
area of California and the Roseburg area of Oregon. 

.^n upper limit to the age of the thrusting is inferred 
from the relation of Late Cretaceous shelf deposits to 
the older superjacent strata. In the Great \'alle\', dep- 
osition of the superjacent shelf deposits was virtually 
conformable into the late Late Cretaceous. In the 
Coast Ranges, however, the relation is one of great 
unconformity at the few places where the late Late 
Cretaceous shelf deposits are known to occur on the 
older shelf and eugeosynclinal rocks. 

Post-Mesozoic structures generally are difficult to 
recognize in the Klamath .Mountains, mainl\- because 
of the scarcity of Tertiary strata in which post-.Meso- 
zoic folds or faults would be readil>' distinguished. 
However, it is apparent that the gross arcuate struc- 
tural pattern of the Klamath .Mountains was estab- 
lished by early Tertiary and that subsequent deforma- 
tion has a different style and was less intense than that 
of the Nevadan and Late Cretaceous. 

The pattern of Cenozoic deformation, however, is 
clearly evident in the area covered b\' the Weaver- 
ville Formation of OIigocene(?) age. This formation, 
the oldest Tcrtiar\- deposit in the southern Klamath 
Alountains, lies unconformably on patches of Creta- 
ceous shelf deposits at some places, but at other places 
nearby it rests directly on Nevadan terrane. This re- 
lation indicates that by 01igocene(?) time the Creta- 
ceous deposits, w hich presumably once mantled much 
of the Nevadan terrane, had been mosth' stripped off. 
It is not clear whether the stripping was accomplished 
principally during the latest Cretaceous or during the 
earliest Tertiarv, but the profound denudation of the 
subjacent terrane may have furnished detritus for the 
Tyee Formation, which is as thick as 10,000 feet and 
is widely distributed in coastal Oregon (Snavelv and 
Wagner, 1964). 

The Weaverville Formation and associated patches 
of Cretaceous rocks are preserved chiefl\' as depressed 
blocks bordered b\' a series of northeast-trending Tcr- 



1966 



Irwin: Klamath Mountains 



37 




Photo 6. View of La Grange fault, looking northeast along U. S. Highway 299 in northwest corner of Weoverville quadrangle. Hillside to iefl 
of highway is exhumed footwoll surface of fault, consisting of Salmon Schist with thin capping of mylonite. Approximate dip-slope trace of fault is 
shown by black line in right background. Rocks in background beyond trace of fault ore chiefly highly-sheared Abroms Schist of hanging-wall block. 



tiary faults. These faults are abundant throughout a 
northeast-trending zone that is at least 30 miles long 
and 10 miles wide. Other Tertiary faults that border 
the Weaverville Formation commonly trend north- 
west. Most of the Tertiary faults appear to be high- 
angle normal faults and some have a vertical displace- 
ment of several thousand feet. 

The La Grange fault, one of the most important 
Tertiary faults, essentially defines the northwestern 
limit of the zone of recognizable northeast-trending 
faults. The footwall surface of this fault is remarkably 
well exposed where it has been exhumed at the La 
Grange hydraulic mine in the northwest corner of the 
Weaverville quadrangle. The fault here forms the 
northern end of the Oregon Mountain outlier of 
Bragdon Formation, which, along with the Abrams 
Mica Schist and the Weaverville Formation constitutes 
the hanging wall block. From the mine the fault ex- 
tends for more than 10 miles northeast, forming the 
northwest boundary of the largest area of Weaver- 
ville Formation, and for most of this distance the foot- 
wall is Salmon Hornblende Schist. 



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?8 



Geology of Northern California 



Bull. 190 



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2396 p. 



METAMORPHIC AND GRANITIC HISTORY OF THE 



KLAMATH MOUNTAINS 

By Gregory A. Davis 
University of Southern California, Los Angeles 



INTRODUCTION 



The orogenic histon^ of the Klamath geological 
province as indicated by the age, duration, and areal 
extent of metamorphic and plutonic igneous events is 
poorly known. Detailed geologic studies of the last 
decade cover only about 25 percent of the California 
portion of the province, largely its central and south- 
eastern areas. High relief, thick vegetative cover, and 
limited accessibility other than by trail has discouraged 
and hindered field work in the Klamath Mountains, 
as has structural complexity and a lack of distinctive 
marker units within many portions of this former 
eugeosynclinal terrane. Nevertheless, as in other for- 
merly neglected areas of "basement rocks," detailed 
field studies coupled with an increasing use of radio- 
metric dating have begun to decipher the Klamath 
geological record — one considerably more complex 
than that envisioned by Diller, Hershey, Hinds, and 
other geological pioneers of the province. 

Following Irwin's terminology (1960) the Klamath 
province can be divided into four arcuate north-south 
lithic belts or subprovinces named from east to west, 
respectively: the eastern Paleozoic, the central meta- 
morphic, the western Paleozoic and Triassic, and the 
^\•estern Jurassic subprovinces (fig. 1). Several revi- 
sions in Irwin's lithic belt designations which appear 
warranted on the basis of recent studies are discussed 
below. 

Regionally metamorphosed rocks of variable grade 
are present in all four Klamath subprovinces, but only 
the central metamorphic and western Paleozoic and 
Triassic subprovinces are composed wholly of meta- 
morphic rocks (exclusive of igneous intrusive bodies). 
Metamorphic relationships within the Klamath Moun- 
tains are complex because of several factors. At least 
two distinct periods of regional metamorphism can be 
recognized in the province, one late Paleozoic and the 
other Jurassic, but the extent of areal overlap between 
the two is unknown. This polymetamorphic history 
coupled with the widespread distribution throughout 
the province of nondistinctive and poorly fossiliferous 
eugeosynclinal parental rocks, for example, cherts, 
shales, and mafic volcanic rocks, makes it difficult, 
without radiometric dating, to assign a particular meta- 
morphic terrane to a particular metamorphic event or 
to correlate one terrane with another. 



Metamorphic relationships between subprovinces are 
further complicated by the tectonic nature of the sub- 
province boundaries. In the southeastern quarter of 
the Klamath Mountains these boundaries are major 
thrust zones bet\\een metamorphic terranes of differ- 
ent grade. Near Cecilville, California (fig. 1), where 
three of the four Klamath subprovinces are tectoni- 
cally superposed, the structural and metamorphic se- 
quence, bottom to top, is as follows: (1) the western 
Paleozoic and Triassic subprovince (lower greenschist 
facies); (2) the central metamorphic subprovince 
(upper greenschist and almandine-amphibolite facies); 
(3) the eastern Paleozoic subprovince (lower green- 
schist facies). Serpentinized peridotites of the sill-like 
Trinity ultramafic pluton separate the eastern Paleo- 
zoic subprovince from the underlying central meta- 
morphic subprovince in this area, as elsewhere over a 
total area of approximately 1,000 square miles. 

EASTERN PALEOZOIC SUBPROVINCE 

Metamorphic relationships in the northern half of 
the eastern Paleozoic subprovince have been previously 
described by Wells and others (1959), Churkin and 
Langenheim (1960), and Davis and others (1965); 
regional metamorphism in the southern half of the 
subprovince has been discussed by Kinkel and others 
(1956) and Albers and Robertson (1961). The bound- 
aries of the subprovince (fig. 1) are essentially those 
defined by Irwin (1960) except for two recently dis- 
covered klippen lying above central metamorpliic 
rocks near Weaverville (Irwin, 1963) and Cecilville 
(Davis, work in progress). 

In the northern part of the subprovince meta- 
morphic relationships are uncertain for lack of detailed 
study. Sedimentary rocks of the oldest known unit, 
the Duzel Formation (Upper Ordovician and/or 
Lower Silurian), exhibit a variable degree of meta- 
morphic recrystallization. Rocks of the formation near 
Callahan exhibit only incipient recrystallization within 
a few hundred yards of some ultramafic contacts. To 
the north and east, however, low-grade metamorphism 
is more complete and muscovite-chlorite-bearing phyl- 
lites, semischists, and phyllitic graywackes are wide- 
spread. Further to the east these rocks overlie unmeta- 
morphosed Middle to Late Silurian sedimentary rocks 
of the Gazelle Formation along the Mallethead thrust 
fault (Churkin and Langenheim, 1960). 



[39] 




Figure 1. Geologic index mop of the Klamath province, northwestern California, showing available Isotopic age data, with inset mop of south- 
western Oregon showing odditionol isotopic oges. Index mop modified offer Weed (1963) and Redding (1962) sheets. Geologic Mop of California. 



[40] 



1966 



Davis: Klamath Mountains 



41 



Sedimentary rocks of the Mississippian Bragdon and 
Kennett Formations in the southern part of the sub- 
province are typically unmetamorphosed, except near 
pluton contacts, but Kinkel and others (1956) report 
that incipient to low-grade regional metamorphisin has 
affected mafic volcanic rocks of the Aiiddle De- 
vonian(?) Copley Greenstone. Volcanic textures in 
Copley greenstones are usually preserved, although 
original mineral assemblages have been replaced by 
chlorite, epidote, albite, and carbonates. The grade of 
greenschist facies nietamorphism and the prevalence 
of foliated rocks decrease eastward. 

Regional nietamorphism of the Copley Greenstone 
under conditions of the greenschist facies should not 
be equated with Late Jurassic albitization of some 
eastern Paleozoic rocks which is described by Kinkel 
and others (1956, p. 74) as "later and . . . unrelated 
in time to the formation of albite in the . . . Copley 
greenstone." Regional albitization and chloritization 
unaccompanied b}- the development of foliation pro- 
duced rocks such as spilites, keratoph\res, and albite 
granites, and affected all Jurassic and pre-Jurassic for- 
mations in the southern part of the province, including 
the Pit River and Mule Mountain granitic stocks. The 
latter stock was albitized after its emplacement into 
metamorphosed and foliated Copley greenstones (Kin- 
kel and others, 1956, p. 47, 57), thus indicating a 
polymetamorphic history for the southern portion of 
the subprovince. 

CENTRAL METAMORPHIC SUBPROVINCE 

Metamorphic rocks \\ithin the central metamorphic 
subprovince were first described by O. H. Hershey 
(1901) as the Abrams Mica Schist and Salmon Horn- 
blende Schist of probable Precambrian age. Studies in 
the Trinity Alps area north of Weaverville b\' Davis 
and Lipman (1962) led to revision of Hershey 's schist 
nomenclature. The Abrams Mica Schist was recog- 
nized as a composite unit including metasedimentary 
rocks both above and below the Salmon Hornblende 
Schist, which were renamed the Grouse Ridge and 
Stuart Fork Formations, respectively. Because the 
Stuart Fork Formation is of lower regional metamor- 
phic grade than the overlying Salmon and Grouse 
Ridge units, Davis and Lipman postulated the Stuart 
Fork-Salmon contact to be a major low-angle thrust 
fault and proposed a tentative correlation of the Stuart 
Fork Formation with low-grade metamorphic rocks 
in the adjacent western Paleozoic and Triassic sub- 
province. Subsequent work by Davis (1964) has con- 
firmed the tectonic nature of the Stuart Fork-Salmon 
contact and the correlation of Stuart Fork rocks with 
those of the western Paleozoic and Triassic subprov- 
ince. Areas of Stuart Fork rocks within the boundaries 
of the central metamorphic subprovince are inter- 
preted as fensters in a regional thrust plate of Salmon 
and Grouse Ridge rocks (fig. 1). 



Detailed accounts of the petrology of the Grouse 
Ridge and Salmon Formations in the central part of 
the central metamorphic subprovince have been given 
by Davis, Holdaway, Lipman, and Romey (1965) and 
by Holdaway (1965). The metamorphic history of 
the Salmon and Grouse Ridge Formations includes 
progressive regional nietamorphism under conditions 
of the upper greenschist and almandine-amphibolite 
facies, and incomplete, static retrogressive nietamor- 
phism under conditions of the lower greenschist facies. 
Rocks of the subprovince are characterized by com- 
plete recr\'staliization, the elimination of primary tex- 
tures and structures, and the development of foliated 
and lineated metamorphic fabrics. 

A simple increase in regional metamorphic grade 
of subprovince rocks from west to east as previously 
described (Davis and others, 1965) is no longer tena- 
ble, although D. P. Cox (Ph.D. thesis, Stanford Univ., 
1956, p. 12-13) has described such a variation in the 
central Helena quadrangle where a calcic albite to 
oligoclase transition is present in Salmon hornblende 
schists. Grouse Ridge rocks in the area east and north- 
east of Cecilville, and most Salmon schists north of 
the Browns Meadow fault, contain clear, primary 
albite and other minerals characteristic of the upper 
greenschist facies. Oligoclase or albite-epidote pseu- 
domorphs of calcic plagioclase, however, are widely 
distributed in recently discovered Grouse Ridge rocks 
south of Cecilville, as well as in those of the t\pe 
locality along the eastern border of the central meta- 
morphic subprovince. 

Regional metamorphism of the Salmon Hornblende 
Schist, and therefore of the Grouse Ridge Formation, 
has been determined bv Lanphere and Irwin (1965) 
as Late Pennsylvanian to Early Permian on the basis 
of three potassium-argon dates on hornblende from 
schists in the Weaverville area (270, 273, and 286 m.y., 
revised dates, M. A. Lanphere, written communication, 
1965). The age and origin of the later, retrogressive 
metamorphic event are not known. 

WESTERN PALEOZOIC AND TRIASSIC SUBPROVINCE 

The few published accounts of metamorphic rela- 
tionships in the western Paleozoic and Triassic sub- 
province include papers by Wells (1956) and Wells 
and associates in southern Oregon (1940, 1949), recon- 
naissance work in California by Irwin (1960), and 
studies of the Stuart Fork Formation within and ad- 
jacent to the central metamorphic subprovince (Davis 
and Lipman, 1962; Davis and others, 1965). Metasedi- 
mentary and metavolcanic rocks of the subprovince 
include, from south to north, the Chanchelulla Forma- 
tion (Hinds, 1933), the Stuart Fork Formation, and 
the Applegate Group (Wells and others, 1949). Be- 
cause of incomplete mapping and a paucity of fossils 
w-ithin rocks of the subprovince, the stratigraphic rela- 
tionships between these units are not known. 



42 



Gfology of Northirn California 



Bull. 190 



Witliin southern Oregon and in tlic Cecilville and 
Helena quadrangles, California (rig. 1), the character- 
istic grade of regional nictaniorphisni is that of the 
lower grccnschist facies (chlorite subfacies). Primary 
tectures and structures are widespread in all rock 
types. Pillow structures, and vesicular, porphyritic, 
and p\roclastic textures arc commonly preserved in 
metabasalts and meta-andesites, although original min- 
eral constituents have been altered to assemblages of 
albite, actinolite, cpidote, chlorite, and carbonates. In 
interlayercd rocks of sedimentary origin the effects of 
metamorphic rccr\stallization are generally most ob- 
vious in limestones (increase in grain size) and argil- 
laceous rocks (development of cleavage). 

Glaucophane- and lawsonite-bearing rocks represen- 
tative of the glaucophane schist facies have been found 
to date at two localities within the subprovince. A 
small isolated outcrop of fine-grained glaucophane- 
lawsonite schist was discovered by D. P. Cox (Ph.D. 
thesis, Stanford Univ., 1956, p. 27) within metasedi- 
mentary rocks in the southwestern corner of the 
Helena quadrangle. The writer has mapped a separate, 
more extensive occurrence of glaucophane-lawsonite 
phyllites, schists, and nonfoliated rocks in the Cecil- 
ville and Helena quadrangles. Here a north-south belt 
of glaucophanitic rocks 1,500-2,000 feet wide and 8-9 
miles long crosses the quadrangle boundary approxi- 
mately I mile west of the fault contact between the 
western Paleozoic and Triassic and central meta- 
morphic subprovinces. The belt is bordered on eastern 
and \\ estern sides by low-grade metasedimentary and 
mafic metavolcanic rocks in which primary textures 
and structures are well preserved and mineral assem- 
blages are those of the chlorite subfacies of the green- 
schists facies. In contrast, rocks within the glaucophane 
schist belt are generally characterized by penetrative 
deformation and most, although not all, are foliated. 
At the northern end of the belt 1 mile north of the 
Salmon-Trinity drainage divide glaucophane-lawsonite- 
bearing rocks grade into sheared greenstones and 
metasedimentar\' rocks. Petrologic study of the rocks 
of the belt is in progress. 

Metarhorphic rocks within the biotite subfacies of 
the greenschist facies arc present in the Sawyers Bar 
quadrangle to the north of the Cecilville quadrangle 
and locally in areas south of Cecilville. Lipman (in 
Davis and others, 1965) reports albite and biotite in 
metacherts in the southern part of the Stuart Fork 
fenster within the central metamorphic subprovince. 
Biotite is also a constituent of schistose metacherts 
within 1,000-2,500 feet of the thrust contact with the 
central metamorphic subprovince in the Cecilville 
quadrangle south of Cecilville. At even greater dis- 
tances (up to 4,000 feet) below the thrust plate re- 
crystallization of metacherts becomes apparent in the 
field and a penetrative slip surface is first noted. Within 
the thrust zone the muscovite-biotite-quartz schists, 
locally phyllonitized, arc tectonically intermixed with 



foliated and unfoliated metavolcanic rocks of the sub- 
province and phyllonitized Salmon hornblende schists. 

The increase in grade of metasedimentary rocks up- 
wards from chlorite to biotite subfacies towards the 
thrust plate can be attributed either to dislocational 
metamorphism within the thrust zone or to thermal 
effects on low-grade rocks produced by the tectonic 
emplacement over them during regional metamorphism 
of a metamorphic sheet of higher temperature (alman- 
dine-amphibolite facies). The biotite in metacherts in 
the southern part of the Stuart Fork fenster may also 
be related to thrust faulting, or it may represent an 
increase to the cast in the grade of regional meta- 
morphism which has affected the subprovince. 

iMost of the northern half of the Sawyers Bar quad- 
rangle lies within a biotite zone in which metasedi- 
mentary and some metavolcanic rocks contain the dis- 
tinctive assemblage of biotite and albite (C. K. 
Seyfert, Ph.D. thesis, Stanford Univ., 1965). Biotite- 
albite-bearing rocks grade northwards into oligoclase 
or andesine-bearing rocks of the almandine-amphibo- 
lite facies. The facies transition approximates in posi- 
tion the northern boundary of the Sawyers Bar quad- 
rangle with the Scott Bar quadrangle. Seyfert (op. cit., 
p. 42) believes that the presence of biotitic meta- 
morphic rocks in the Sawyers Bar quadrangle is "at 
least in part" due to the large number of granitic plu- 
tons in the area, but the continued increase in grade 
to the north, where granitic plutons are absent, is 
indicative that the variation is predominantl\- regional 
in nature and independent of subsequent plutonism. 

W. P. Pratt (Ph.D. thesis, Stanford Univ., 1964) 
reports that the assemblage andesine (or oligoclase)- 
homblende-epidote is representative of mafic metavol- 
canic rocks found throughout the Marble Mountains 
area in the Scott Bar quadrangle. In man_\' of the mafic 
metavolcanic rocks relict porphyritic and pyroclastic 
textures are present, although most rocks of both sedi- 
mentary' and volcanic origin have a faint to well-de- 
veloped foliation. A general increase in the degree of 
foliation development eastwards across the quadrangle 
is reported by Pratt (op. cit., p. 79), but even within 
foliated sequences there are structural domains in 
which foliation is absent or onl\' poorK' developed and 
relict textures and structures are preserved. Retrogres- 
sive effects of a localized nature, including the saus- 
suritization of plagioclase, are noted b>' Pratt in some 
rocks of the Marble Mountains terrane. 

In summary, rocks of the western Paleozoic and 
Triassic subprovince within California increase in 
regional metamorphic grade northwards across the 
Helena, Cecilville, Sawyers Bar, and Scott Bar quad- 
rangles from the lower greenschist facies to the 
almandine-amphibolite facies. No major structural 
breaks across this portion of the subprovince have been 
mapped so that metasedimentary and metavolcanic 
rocks within this area probably constitute a continu- 
ous terrane from the structural standpoint. In the 
writer's opinion, however, the extension of the sub- 



1966 



Davis: Klamath AIoumains 



43 




Photo 1. Trinity Dam. Photo by Phil Merril. 



44 



ClOI.OCY OK NoRTlll RN CaI.IKORNIA 



Bull. 190 



province to tiic cast of tlic Scott B;ir quadrangle and 
nortli to the t>pc ;irea of the Applegatc Group in 
southern Oregon has not \'ct been demonstrated, .^c- 
cordingl\-, nietaniorphic and structural relationships 
u ithin the area which includes the Seiad Valle\-, Con- 
drc>' Mountain, and Fort Jones 15-niinute quadrangles, 
California, and the southern portions of the M)-niinutc 
Grants Pass and .Medford quadrangles, Oregon, are 
described separately below . 

SEIAD VAUEY-CONDREY MOUNTAIN-FORT JONES AREA 

The w Titer is indebted to Preston K. Hotz and to 
Cjordon L. iMedaris, whose work in the Condre>- 
.Mountain and Seiad Vallc\- quadrangles, respectively, 
is in large part the basis for the following discussion; 
both studies are in progress at the time of this writing 
and findings reported herein are subject to revision. 

.Approximately 2.50 square miles of the central part 
of the Seiad \'allev-Condre\' .Mountain area along the 
Oregon-California border are underlain by highl\' 
foliated, low-grade schists of the greenschist facies 
(fig. I). This schist unit, which appears to be the 
lowermost unit in the region in a structural sense, has 
been previously referred to as the "old schists" (Wells 
and others, 1940) and the "pre-Upper Triassic schists" 
(Wells, 1956). Hotz (written communication, 1965) 
de.scribes rocks of the unit as of two main types: 
quartz-muscovite schists, commonly graphitic, and 
chlorite-actinolite-epidote schists. The age of the 
schists, as for all metamorphic rocks in the vicinit\-, is 
unknown. 

The low-grade schists are apparently completely 
surrounded and in tectonic contact with metavolcanic 
and metascdimentary rocks assignable to the alman- 
dine-amphibolite facies. These higher grade rocks in- 
clude in the Condrey Mountain quadrangle a lower 
member of oligoclase or andesine-bearing hornblende 
schists and an upper, largely metasedimentary, mem- 
ber of muscovite-biotite phyllites and .schists, quartz- 
ites, marbles, and hornblende schists. Both members 
are extensively intruded by serpentinized ultramafic 
rocks, in contrast to the central greenschist terrane 
which is nearl\' barren of ultramafic intrusions. Horn- 
blende schists in the northeastern corner of the Scott 
Bai quadrangle mapped by Pratt (Ph.D. thesis, Stan- 
ford Univ., 1964) as the Town.send Gulch Schist 
probably occup\' a structural position comparable to 
the lower member of hornblende schists in the Con- 
drey Mountain quadrangle. 

Hotz (written communication, 1965) describes the 
contact between the low-grade schists and the higher 
grade rocks to the east as a moderate to stceph' dip- 
ping reverse fault along w hich the higher grade rocks 
have moved over the schists of greenschist facies. 
Medaris (personal communication, 1965) reports that 
the western contact of the greenschist terrane with 
ultramafic rocks, hornblende schists, and amphibolites 
north of Seiad Valley is a west-dipping fault. 



Boundary relationships of the high-grade rocks with 
metamorphic units at greater distances from the green- 
schist terrane are not >et completely clear. Amphibo- 
lites in the Seiad Valley area appear to grade down- 
wards into cpidotc-hornblende schists of lower 
metamorphic grade and upwards into low-er grade 
rocks of the .\pplcgate Group (Medaris, personal 
communication, 1965). A transition between rocks of 
the .Applcgate Group and rocks of the almandine- 
amphibolite facies in the Grants Pass quadrangle north 
of the greenschist terrane has also been reported by 
Wells (1956). In the Condrey .Mountain area the high- 
grade rocks are overlain, along a thrust fault in the 
few areas where the contact is exposed and is not oc- 
cupied by igneous intrusions, by interlayered meta- 
volcanic and metasedimentary rocks of similar grade 
which pass eastwards and southwards into weakly 
metamorphosed argillites, slates, cherts, and mafic vol- 
canic rocks (Hotz, written communicarion, 1965). 
These low-grade rocks probably extend southwards 
into the Fort Jones quadrangle where the\' arc in fault 
contact, approximate!)' along the Scott Bar-Fort Jones 
quadrangle boundar\-, with the high-grade rocks of 
the Marble .Mountains area described above. They 
have been correlated with the Applegate Group by 
Wells and others (1959) and included within the west- 
ern Paleozoic and Triassic subprovince by Irwin 
(1964), although neither correlation can as yet be 
prosed. 

In summary, a highlv foliated, low-grade metamor- 
phic terrane (greenschist facies) along the Oregon- 
California border is surrounded tectonicalh', and pos- 
sibly overlain, by higher grade mctanK)rphic rocks 
(almandine-amphibolitc facies). A gradation outwards 
from rocks of the almandinc-amphibolite facies to 
weakly metamorphosed volcanic and sedimentar\- 
rocks is reported to the west, north, and east of the 
central greenschist terrane, although structural rela- 
tionships between the high-grade and outer low-grade 
rocks apparently vary. If metasedimentary and meta- 
\()lcanic rocks of the almandine-amphiobolite facies in 
the Marble .Mountains overlie the Townscnd Gulch 
Schist, as Pratt postulates (Ph.D. thesis, Stanford Univ., 
1965), then the decrease in grade of regional meta- 
morphism south of the .Marble .Mountains may be of 
similar nature to that noted on all other sides of the 
central greenschist terrane. 

The central greenschist or "old schists" terrane has 
l)ecn correlated with the central metamorphic sub- 
province by Irwin ( 1960, 1964), although its structural 
position and metamorphic grade are not those this 
writer would expect if the correlation is valid. Irwin 
( 1964) has assigned the higher grade rocks which bor- 
der (and overlie?) the central terrane to the western 
Paleozoic and Triassic subprovince. Gradations re- 
ported between rocks of tlie almandine-amphibolitc 
facies and lower grade rocks of the .\pplegate Group 
in the Seiad V'alley and Grants Pass quadrangle sup- 



1966 



Davis: Klamatii Mountains 



45 



port this correlation, but additional confirmation of 
the gradational relationship is needed in light of con- 
flicting relationships elsewhere. 

Sequential and petrologic similarities exist t)et\\ecn 
rocks of the almandine-amphibolite facies of tlie Scott 
Bar, Condrey Mountain, and Seiad \'alley quadrangles, 
and the Salmon-Grouse Ridge sequence of the central 
metamorphic subprovince. It is doubtful, however, 
that the two areas of high-grade rocks are at present 
structurally continuous, although the possibilit\' does 
exist that both metamorphic sequences were originall\' 
derived from common parental rocks during the same 
metamorphic event. Lack of structural continuity be- 
tween the two areas is indicated by the observation 
that low-grade rocks which appear to grade into or 
to overlie the northern high-grade terrane are over- 
thrust by rocks of the central metamorphic sub- 
province near Cecilville, and probably along the south- 
ern boundar\- of the Condrev Mountain quadrangle 
(fig. 1). 

WESTERN JURASSIC SUBPROVINCE 

The western Jurassic subprovince, within California 
the least studied of the four Klamath subprovinces, 
was defined by Irwin (I960) to include the Galice 
Formation of middle Late Jurassic age and what he 
believed to be its locally developed metamorphic 
equivalents, the South Fork Mountain, Weitchpec, 
Kerr Ranch, and Colebrooke schists. A thick sequence 
of volcanic and metavolcanic rocks below sedimentary 
and metasedimentary rocks of the Galice Formation 
is particularly well developed in southwestern Oregon. 
This sequence was originally mapped by Wells and 
Walker (1953) as the Rogue Formation, but was later 
included within the Galice Formation bv Cater and 
Wells (1954). 

The position of the western boundary of the sub- 
province, and hence the western boundary of the 
Klamath province, is still subject to question. R. H. 
Dott, to whom appreciation is extended for the use 
of material unpublished at the time of this writing, 
has presented strong evidence (1965) that the Dothan 
Formation of southwestern Oregon properly belongs 
to the western Jurassic belt and is probably older than 
the Galice Formation \\'hich borders it to the east (fig. 
1). Dott's position, accepted in this paper, contrasts 
with that of Irwin ( 1960, 1964) who assigns the Dothan 
Formation to the Coast Range province. 

Within California the western boundary of the sub- 
province is drawn by Irwin (1960, 1964), to include 
a narrow, fault-bounded belt of low-grade schists, the 
South Fork iMountain Schist, which separates Fran- 
ciscan rocks on the northern Coast Ranges from Ga- 
lice(?) rocks for nearly 120 miles (fig. 1). Serpen- 
tinized ultramafic rocks are present along much of 
the eastern fault contact of both the South Fork 
Mountain Schist and similar schists which extend 
southward from South Fork Mountain along the west- 
ern side of the Sacramento Valley. These schists, at 



least from South Fork Alountain to the south, gen- 
erall\' have lawsonite- and aragonite-bearing mineral 
assemblages characteristic of the glaucophane schist 
facies (Blake and Ghent, 1964; Ghent, 1965). Irwin 
(1960, p. 29) assigns the South Fork Mountain Schist 
to the Klamath province since schists exposed near 
Weitchpec and believed to be the northern part of 
the South Fork Mountain belt grade into slates and 
ph\'llites correlated with the Galice Formation. At 
the southern end of the belt, however, Ghent (1965) 
believes that the .schists of South Fork Mountain are 
continuous with tho.se to the south which he and 
others, including Irwin (I960, fig. 3), tentatively assign 
to the Franciscan Formation. The metamorphism of 
these southern schists is younger than Klamath meta- 
morphic events dated elsewhere. Blake and Ghent 
(1964, p. 31) report that "Late Jurassic and Early 
Cretaceous fossils were found in lawsonite- and 
aragonite-bearing metagraywackes at four separate 
localities, indicating a post-Early Cretaceous period of 
metamorphism." 

Throughout the western Jurassic subprovince the 
presence of slates, phyllites, and altered graywackes 
and volcanic rocks attests to widespread, but low-grade 
regional metamorphism. Locally, higher grade and 
more thoroughly recrystallized rocks are found, in- 
cluding schists, gneisses, and amphibolites. Gradations 
between such rocks and parental rocks in the Dothan 
and Galice Formations have been described in a num- 
ber of areas. In the Collier Butte-Agness area of south- 
western Oregon micaceous and chloritic schists of the 
Colebrooke Formation grade southward across the 
Rogue River into sandstones, mudstones, conglomer- 
ates, and greenstones of the Dothan Formation (Dott, 
1965). Metamorphism of the Colebrooke Formation 
has been radiometrically dated at 138 m.y. (whole 
rock potassium-argon date on quartz-mica schist; 
Dott, 1965). This Late Jurassic date is in agreement 
\\ith other limiting evidence on the time of metamor- 
phism: a radiometric age of unmetamorphosed Dothan 
rhyolite of 149 m.y. (whole rock potassium-argon; 
Dott, 1965), and the unconformable relationship be- 
tween Colebrooke metamorphic rocks and unmeta- 
morphosed late Late Jurassic (Portlandian) conglom- 
erates of the Myrtle Formation in an area about 25 
miles north of Agness (R. H. Dott, Jr., written com- 
munication, 1965). 

In the 15-minute Galice quadrangle, Oregon, to the 
northeast of the Collier Butte area, low-grade, mafic 
to silicic metavolcanic rocks of the Rogue Member of 
the Galice Formation grade into amphibole gneisses, 
quartz schists, and quartz-garnet-mica gneisses with 
mineral assemblages characteristic of the upper green- 
schist and almandine-amphibolite facies (Wells and 
Walker, 1953). These rocks extend southward into the 
30-minute Kerby quadrangle, Oregon, where they 
were originally described as being older than the Ga- 
lice Formation and possibly correlative with high-grade 
metamorphic equivalents of the Applegate Group in 



46 



Gf.ology of Northf.rn California 



Bull. 190 



the Medford quadrangle (Wells and others, 1949). 
Their subsequent recognition as inctaiiiorphic equiva- 
lents of the Galice Formation points f)ut the difficulties 
of correlating one metaniorphic unit with another 
solely on the basis of petrologic similarities. 

REGIONAL METAMORPHISM AND UlTRAMAFIC INTRUSIONS 

A recurring problem in Klamath geological studies 
and one of importance in this discussion is the rela- 
tionship between metamorphism of regional type and 
the intrusion of ultramafic rocks. The problem arises 
from the close spatial association of most of the higher 
grade Klamath metaniorphic tcrranes with ultramafic 
intrusions, although ultramafic rocks also intrude 
Klamath terrancs \\hcre metamorphism has not oc- 
curred or is only of low grade. As examples of the 
former association, schists, gneisses, and amphibolitcs 
of the almandine-amphibolite facies are bordered or 
extensively intruded by ultramafic rocks in the Galice 
and Kerby quadrangles in the western Jurassic sub- 
province, in the Condrey Mountain-Seiad Valle\- 
Marble Mountains area, and in the central metaniorphic 
subprovince (Grouse Ridge Formation). 

It is the variability of contact relationships hetw een 
ultramafic and surrounding country rocks both on a 
regional scale and in given local areas, that has ob- 
scured possible genetic relationships between ultramafic 
intrusions and the foliated metaniorphic rocks which 
border them at some localities. For example, high- 
grade metaniorphic equivalents of the Galice Forma- 
tion in the Galice and Kerby quadrangles are present 
only along the contacts of a narrow apophysis of the 
extensive Josephine peridotite sheet. Nevertheless, the 
metamorphic rocks are only discontinuously present 
along the apoph\sis (Wells and others, 1949); there is 
no consistent relationship between width of the apoph- 
ysis and width of the belt of metaniorphic rocks (up 
to 2 miles), and similar rocks are not found adjacent 
to other apophyses of the same pluton in this area. 
Metamorphic eflFects are not present in Galice rocks 
along the main contact of the Josephine pluton in the 
Gasquet quadrangle of California immediately to the 
south (Cater and Wells, 1954, p. 98, 112). 

The most striking spatial association between ultra- 
mafic intrusions and metaniorphic rocks of moderate 
to high grade is in the metamorphic terrane which sur- 
rounds the low-grade "old .schists" of the California- 
Oregon border area (see, for example, the geologic 
map of the Medford quadrangle, Oregon, Wells, 19.') 6, 
or the Weed sheet of the Geologic Map of Califor7iiii, 
Strand, 1963). C. K. Seyfert (Ph.D. thesis, Stanford 
Univ., 1965, p. 166) has postulated that the presence 
of rocks of the almandine-amphibolite facies in the 
Marble Mountains of the Scott Bar quadrangle may 
be due to metamorphic effects from the numerous 
large ultramafic bodies in the area. W. P. Pratt (Ph.D. 
thesis, Stanford Univ., 1964, p. 74), however, has con- 
cluded that intrusion of the major ultramafic bodies 



in the Scott Bar quadrangle probably postdated re- 
gional metamorphism. 

Near Sciad Valley the metamorphic grade in meta- 
volcanic rocks increases both up and down structure 
towards a large sill-like peridotite body in the Red 
Butte-Kangaroo Mountain area (G. Medaris, per- 
sonal communication, 1965). Amphibolites (alman- 
dine-amphibolite facies) surround the largely unser- 
pcntinized ultramafic body on all sites except along 
the eastern fault contact with the "old schists," and 
p\roxene granulites are locally developed at the in- 
trusive contact. Medaris believes that there is a close 
time relationship between regional metamorphism, 
penetrative deformation of the metamorphic rocks, 
and ultramafic emplacement in the Seiad Valley area, 
and that the higher grades of metamorphism are very 
likel\- related to the peridotite intrusion at Red Butte. 
The amphibolitic rocks which border the peridotite 
appear to this writer to be very similar to recrystal- 
lized hornblende schists found within contact aureoles 
of some granitic plutons in the central metamorphic 
subprovince. 

One of the largest ultramafic bodies in the Klam- 
ath province is the sheetlike Trinity pluton which 
separates the central metamorphic and eastern Paleo- 
zoic subprovinces. Lipnian (1964) has postulated that 
contact metamorphism acting downward from the 
Trinit>' pluton might account for metamorphic rela- 
tionships observed below the peridotite sheet, princi- 
pally (1) the lower grade of the Stuart Fork Forma- 
tion as opposed to that of overlying units, and (2) 
the coarser grain size of Grouse Ridge amphibolites as 
compared with Salmon schists of comparable compo- 
sition. A tectonic alternative for explaining these rela- 
tionships has been offered elsewhere (Davis and others, 
1965), although Hershey (1901, p. 240) considered the 
problem of metamorphism of country rocks by the 
Trinity pluton in another light — the absence of meta- 
morphism or appreciable metamorphism of eastern 
Paleozoic rocks (his "Devono-Carboniferous" series) 
above the ultramafic pluton. In Hershey's words: 

"It would be too remarkable a cose of selection to suppose that 
the peridotyte converted thousands of feet of stroto into mica and 
hornblende schists in one area, and that in an immediately adjoin- 
ing area . . . failed to develop . . . even a norrow contact zone 
of similar schist. The inference is unavoidable that the schists ore 
a distinct series, as a whole much more highly metamorphosed than 
the Devono-Carboniferous, and that at leost to the extent that their 
alteration exceeds that of the other series, the metamorphism is 
not due to the intrusion of peridotyte." 

The mobility of ultramafic rock masses, during 
primary emplacement and secondary or "cold" intru- 
sion related to later deformation, seriously complicates 
metamorphic-ultramafic relationships. The absence of 
a metamorphic contact zone along a particular ultra- 
mafic contact can be attributed, for example, to dis- 
ruption and "erosion" of contact rocks by primary or 
secondary movements within the ultramafic body 
(cf. P. W. Lipman, Ph.D., thesis, Stanford Univ., 
1962, p. 67), or alternatively, to a location at present 



1966 



Davis: Klamath Mountains 



47 



of the ultramafic rocks which has resulted from sec- 
ondary intrusion and is far removed from the original 
site of emplacement where metamorphic effects might 
be found. 

There appears to be no consistent relationship be- 
tween the development of foliated metamorphic rocks 
and the degree of serpentinization of ultramafic bodies 
in contact ^\■ith them. In the Kerby quadrangle ser- 
pentinites and unserpentinized peridotites occur in 
contact with both metamorphosed and unmetamor- 
phosed rocks of the Galice Formation (Wells and 
others, 1949, map). Ultramafic intrusions within 
gneisses and amphibolites in the Medford quadrangle 
are predominantly serpentinized (Wells, 1956), whereas 
metamorphic rocks of similar grade and structural 
position in the Seiad Valley area are intruded by perid- 
otites which are largely unserpentinized. These vari- 
able relationships ma>' result' from factors difficult to 
assess, such as the extent and effects of secondary in- 
trusion, or the size, shape, and level of exposure of 
partly serpentinized ultramafic bodies. 

It is the writer's opinion, and one which will no 
doubt be contested, that the variations in regional 
metamorphic grade previously noted for the three 
easternmost Klamath subprovinces and the Seiad 
Valle\'-Condrey Mountain area are due to factors op- 
erative prior to ultramafic emplacement in these areas 
and unrelated to it. Localized upgrading of regionally 
metamorphosed rocks by contact metamorphism does 
appear to have occurred adjacent to some large and 
predominantly unserpentinized peridotitic plutons, as 
for example, in the Seiad Valley area and adjacent to 
the Josephine pluton in the Kerby and Galice quad- 
rangles (although in this latter example tectonic and 
intrusive complications of original contact relation- 
ships bet\veen ultramafic and metamorphic rocks ap- 
pear likely). 

GRANITIC INTRUSIONS 

Granitic intrusions are present throughout the 
Klamath province, but particularly concentrated 
within a central or axial zone which excludes most of 
the western Jurassic and eastern Paleozoic subprov- 
inces (fig. 1). The plutons of the province are typi- 
cally of dioritic, quartz-dioritic, or granodioritic com- 
position, although gabbros and quartz monzonites 
represent compositional extremes present in some 
intrusions. Compositional variations within single plu- 
tons have been attributed by different authors to mul- 
tiple intrusion, assimilation of wall rocks, and mag- 
matic differentiation /w situ and at depth prior to 
emplacement. Many of the larger Klamath plutons 
are composite bodies, with the outer intrusive units 
characteristically the oldest and most mafic in compo- 
sition. 

Within the central metamorphic subprovince the 
rocks of most plutons exhibit much higher Na20/K20 
ratios than do calc-alkaline granitic rocks of compar- 
able silica percentage from the Sierra Nevada batho- 



lith. Reasons for this differentiation trend toward 
sodic rocks of trondhjemitic composition have been 
discussed by Moore (1959), Davis (1963), and Lipman 
(1963), but the matter is at present unresolved, as is 
the areal extent within the Klamath Mountains of such 
differentiation. The English Peak batholith in the 
Sawyers Bar quadrangle, for example, exhibits a nor- 
mal calc-alkaline trend of compositional variation from 
gabbros to quartz monzonites (C. K. Seyfert, Ph.D. 
thesis, Stanford Univ., 1965). 

Granitic plutons in the Klamath Mountains are 
generally aligned with their long axes parallel to the 
north-south arcuate trend of the province. Their pre- 
dominant mode of emplacement as indicated by 
largely concordant contacts and the deflection of 
country rock structures around them was by force- 
ful intrusion. Most of the more equidimensional plu- 
tons studied to date are domical in internal form (cf. 
Davis and others, 1965, pi. 1). The more elongate 
plutons, which seem particularly characteristic of the 
western Paleozoic and Triassic subprovince, are prob- 
ably sheetlike in shape. One such dioritic intrusion in 
the Kerby quadrangle is described by Wells and 
others (1949) as a sill, 20 miles long, 'l 3,000-20,000 
feet thick, and dipping to the east at approximately 
60°. The sill has been emplaced along the contact zone 
between the Dothan Formation and the overlying Jo- 
sephine peridotite sheet. Another sill-like granitic plu- 
ton, ranging from gabbro to quartz diorite in compo- 
sition, is present in the southern part of the Condrey 
Mountain quadrangle (P. Hotz, written communica- 
tion, 1965). This southward-dipping intrusion also 
follows a major contact, probabh' a thrust fault, be- 
tween hornblende schists and higher, weakly meta- 
morphosed sedimentary and volcanic rocks. 

On the basis of general geological relationships the 
age of the granitic plutons in the Klamath Mountains 
has been considered as Late Jurassic or Early Creta- 
ceous by most geologists (cf. Irwin, 1960). Recent 
potassium-argon age dating of Klamath granitic rocks 
has partly supported this supposition, but has also re- 
vealed the presence within the province of granitic 
rocks considerably older than Late Jurassic. 

The existence of \\idespread plutonism in the Klam- 
ath province during the Late Jurassic is indicated by 
potassium-argon dates from rocks of granitic plutons 
in the central metamorphic subprovince and the west- 
ern Jurassic subprovince in southwestern Oregon 
(fig. 1). Six biotite-determined dates on five plutons 
in the former subprovince range from 125 m.y. to 140 
m.y. (Davis and others, 1965); across the Klamath 
province in southwestern Oregon, Dott (1965) reports 
dates of 130 m.y., 141-145 m.y. (biotite), and 151 
m.y. (hornblende) for the diorites of the Grizzly 
Mountain, Pearse Peak, and Collier Butte plutons, re- 
spectively. Four of the six dates determined from 
biotites in granitic rocks of the central metamorphic 
subprovince are Early Cretaceous using Kulp's 1961 
time-scale, but geological relationships would seem to 



48 



Gkology of N()rtiii-,rn California 



Bull. 190 



require that c\cii the youngest of the dated plutons, 
the Shasta Bally batholith. be Late Jurassic in age 
(Irwin, 1960, p. 57-5S). Recent studies on potassium- 
argon dating of hiotitc have indicated that biotite ages 
are t\picall\- sounger and geologicall\- less reliable 
than dates from hornblendes in the same specimens 
(Kistier and others, 1965; Hart, 1964). 

Hornblende-determined pre-Jurassic dates on dio- 
ritic rocks in the northwestern and southeastern cor- 
ners of the Klamath province, together with similar 
radiometric ages for the Salmon Hornblende Schist 
in the central meramorphic subprovince, indicate an 
earlier Klamath orogenic episode of unexpectedh- 
broad areal extent. Hornblende from the Pit River 
Diorite in the southern part of the eastern Paleozoic 
subprovince has been dared as Early to Aliddle Tri- 
assic in age (218 m.y., Evans, 1965). A comparable 
early age for the nearby .Mule Mountain stock appears 
reasonable, since both it and the Pit River stock were 
regionally albitized prior to Late Jurassic emplacement 
of the Shasta Ballv batholith (Kinkel and others, 1956, 
p. 47). 

Horneblende dates of 285 m.y., 275 m.y., and 215 
m.\-. are cited b\- Dott (1965) for the Saddle Moun- 
tain Diorite, the Pcarse Peak Diorite, and a mafic dike 
rock in southwestern Oregon, respectivel\-. The dates 
appear to be anomalousl\- old for rocks apparently 
intrusive into the western Jurassic subprovince, but 
their striking similarit\- to dates on the Pit River Di- 
orite and the Salmon Hornblende Schist (286 m.y. to 
218 m.\-.) lends them credence. Dott (1965) has sug- 
gested that the dike rock and the Saddle Mountain 
Diorite ma\- be old crustal material brought up along 
fault zones in the ultramafic rock with which thev 
are associated. Field relationships of the Pearse Peak 
Diorite, however, are described by Dott as inconsis- 
tent with this explanation. .\n alternative explanation 
for the Pearse Peak pluton is that dioritic basement 
rocks of Paleozoic age were remobilized and intruded 
to higher crustal levels during Late Jurassic orogeny. 
This possibility would be in accord with the \ounger, 
biotite-defined age for the Pearse Peak pluton (141 
m.y. to 145 m.y.) and other radiometric evidence for 
Late Juras.sic metamorphism and igneous intrusion in 
the southwestern Oregon area. 

CONCLUSIONS 

Too little is \et known, as the preceding discussion 
shows, to draw an adequate synthesis of the meta- 
morphic and plutonic histor\- of the Klamath Moun- 
tains. The incomplete picture which has begun to 
emerge, however, is of two major provincewide pe- 
riods of regional metamorphism, deformation, and 
igneous intrusion — the first broadly dated isotopically 
as Late Penns\lvanian to E^irl\- or Middle Triassic, 
and the second as Late Jurassic. 

The existence of the older orogenic period in the 
westernmost part of the province can at present only 



be inferred from several anomaloush- old radiometric 
dates, but acro.ss the province mctamorphic rocks of 
the central metamorphic subprovince are Late Pcnn- 
sylvanian to Early Permian in age on the basis of 
limited isotopic age data. The original extent of the 
metamorphic terrane of which the Salmon and Grouse 
Ridge Formations are part cannot be determined with 
certaintN', since the central metamorphic subprovince 
is an allochthonous plate which overlies the western 
Paleozoic and Triassic subprovince and is in turn over- 
lain by the eastern Paleozoic subprovince. Neverthe- 
less, a tentative reconstruction of the Late Paleozoic 
metamorphic terrane can be hazarded in the limited 
light of present knowledge, with the admitted possi- 
bilit\ that future studies, particularl\- geochronologic, 
may require its revision. 

in the southeastern Klamath Mountains south of 
hit 41° 15' N., a broadly symmetrical terrane can be 
discerned in which metamorphic grade generally de- 
creases to the east and to the w est from the almandine 
and staurolite zones of regional metamorphism in the 
central metamorphic subprovince. Rocks of the west- 
ern Paleozoic and Triassic subprovince are only in- 
cipientl\' metamorphosed in the westernmost portions 
of the Helena and Cecilville quadrangles, metamor- 
phosed to chlorite zone assemblages to the east, and 
possibly regionally metamorphosed to biotite zone 
assemblages in the Stuart Fork fenster farther east. 
In the southern part of the eastern Paleozoic sub- 
province chlorite zone assemblages in the Copley 
Greenstone are more widespread in western areas 
than in eastern. 

This crude, but apparently real s\nimetry of de- 
creasing metamorphic grade in rocks to both east 
and west f)f the central metamorphic subprovince is 
indicative that rocks of all three subprovinces were 
affected by the Late Paleozoic regional metamorphism 
dated in rocks of the central subprovince. The mini- 
mum east-west width of the postulated Late Paleozoic 
metamorphic terrane prior to its disruption and tele- 
scoping by westward thrusting must have been on 
the order of 50 miles, although the absence of some 
zones in this reconstruction, e.g. the biotite zone be- 
tween the central metamorphic and eastern Paleozoic 
subprovinces, suggests that the terrane was substan- 
tialh' wider. In the Cecilville area minimum thrust 
displacements of the central metamorphic and eastern 
Paleozoic subprovinces are estimated by the w riter to 
be 15-20 and 20 miles, respectiveh'. 

If, to the contrary, regional metamorphism in the 
western Paleozoic and Triassic and eastern Paleozoic 
subprovinces was Late Jurassic in age, as has gcnerall\' 
been believed, then the older rocks of the central meta- 
morphic subprovince between them do nor clearly 
exhibit its effects. Retrogressive mineral assemblages 
are present in rocks of the central subprovince, but 
the\- are only incompletely developed — particularl\- so 
in the lower subprovince unit, the Salmon Hornblende 



1966 



Davis: Klamath Mountains 



49 



Schist. In addition, retrogression was not accompanied 
by the penetrative deformation responsible for the 
development of foliated rocks in the adjoining sub- 
provinces. If rock units in the eastern Paleozoic sub- 
province were not regionally metamorphosed until the 
Late Jurassic, as Kinkel and others claim (1956, p. 65), 
then it is difficult to explain the absence of earlier 
metaniorphic effects on Paleozoic units, such as the 
Cople\' Greenstone, which are older than the dated 
metamorphic event in the central metamorphic sub- 
province. The absence in the southeastern Klamath 
area of other rocks belonging to the Late Paleozoic 
terrane only partially represented by the moderate to 
high-grade Salmon and Grouse Ridge Formations is 
also difficult to explain in terms of Jurassic regional 
metamorphism only of the adjacent subprovinces. 
These problems can be resolved if the metamorphic 
rocks of the three subprovinces are considered to 
represent disrupted portions of a single Late Paleozoic 
terrane. 

Late Paleozoic regional metamorphism of the Cop- 
ley Greenstone does not seem at odds with knoA\'n 
geological relationships, and Irwin (1960, p. 20) has 
previously commented on the possibility that the 
Salmon Hornblende Schist and Copley Greenstone 
were metamorphosed at the same time. As described 
above, regional metamorphism of the Copley Green- 
stone under conditions of the greenschist facies pre- 
ceded both Late Jurassic regional albitization and the 
earlier emplacement (Triassic?) of the Mule Moun- 
tain stock. 

Detailed structural and petrologic studies of the 
Stuart Fork Formation of the western Paleozoic and 
Triassic subprovince indicate that its regional meta- 
morphism and accompanying deformation were con- 
temporaneous with that of the Salmon and Grouse 
Ridge Formations (Davis and others, 1965). The prin- 
cipal barrier to accepting Late Paleozoic metamorph- 
ism of the western Paleozoic and Triassic subprovince 
is the presumed Triassic age of many of its rocks. 
Despite its name, however, the writer can find no 
reference to undoubted Triassic rocks within the Cali- 
fornia portion of the subprovince, and direct correla- 
tion of subprovince rocks within California with 
poorly dated rocks of the Upper Triassic(?) Apple- 
gate Group of southern Oregon (Wells and others, 
1949) has not yet been demonstrated. Fossiliferous 
rocks within the subprovince are not abundant, but 
Late Pennsylvanian(?), Early Permian, and Middle or 
Late Permian fossils have been found at several Cali- 
fornia localities (Irwin, 1960, p. 26; 1963). A Silurian- 
Devonian fossil occurrence about 10 miles west-north- 
west of Cecilville has been described by Merriam 
(1961). Irwin (1960, p. 26) reports the presence of 
fossiliferous iMiddle or Late Triassic rocks at the ex- 
treme southern end of the subprovince, but the struc- 
turally complex area of the locality has been mapped 
only in brief reconnaissance and cannot, in the writer's 
opinion, be shown to be structurally continuous with 



that portion of the western Paleozoic and "Triassic" 
subprovince discussed above (fig. 1). 

The disruption of the postulated Late Paleozoic 
metamorphic terrane b>' westward thrust faulting, and 
the emplacement of the Trinit\- ultramafic sheet be- 
tween the central metamorphic and eastern Paleozoic 
thrust plates during thrusting are believed by the 
writer to have occurred during late stages of the Late 
Paleozoic metamorphism. An upper age limit on 
thrusting of the eastern Paleozoic plate is tentatively 
established by the Early to Middle Triassic age of the 
Pit River stock w hich intrudes ILarly Permian lime- 
stones of the plate, although it could be argued that 
the stock is part of the plate. iMiddle and (or) Late 
Triassic to Middle Jurassic stratigraphic units are 
present in the eastern Paleozoic subprovince, but are 
separated from Middle Permian rocks of the plate by 
a probable disconformity (Dott, 1961, p. 578), the 
hiatus of which brackets the time of intrusion of the 
Pit River stock. South of Lake Shasta the Pit Forma- 
tion (Middle and or Late Triassic) is reported to 
overlie the Dekkas Andesite (Middle and L'pper(?) 
Permian) "with apparent structural discordance" by 
Albers and Robertson (1961, p. 35), although these 
authors believe the Dekkas Andesite-Bull\' Hill Rh>o- 
lite-Pit Formation sequence in the East Shasta Lake 
area to be conformable. 

Briefly, evidence for concluding contemporaneity of 
late stages of regional metamorphism, thrust faulting, 
and emplacement of the Trinity pluton includes: the 
crystalloblastic fabric of Salmon phyllonites in the 
basal thrust zone of the central metamorphic plate, 
apparent structural homogeneity between Salmon 
schists within the plate and their ph>'llonitic equiva- 
lents at its base, an increase in metamorphic grade of 
low-grade rocks immediately below the central plate, 
and the incorporation of serpentinites from the Trin- 
ity ultramafic sheet within Grouse Ridge rocks prior 
to cessation of regional metamorphism under condi- 
tions of the almandine-amphibolite facies. The last 
relationship is particularly important in ascertaining 
the age of the Trinit>- pluton, previously considered 
Late Jurassic in age (Irwin, 1960; 1964) because ultra- 
mafic rocks intruded the Galice Formation in the 
western Jurassic subprovince at that time. Ultramafic 
intrusion in central and northeastern Oregon, however, 
can be dated stratigraphically as post-Early Permian 
and pre-Late Triassic (Thayer and Brown, 1964, p. 
1257). Emplacement of ultramafic and gabbroic rocks 
in Oregon during this interval was associated with 
regional metamorphism and "w as followed closely by 
intrusion of quartz diorite and albite granite" (ibid.. 
p. 1257). A close parallel can thus be drawn between 
metamorphism and Permo -Triassic intrusive activit\' 
in Oregon, and metamorphism and a presumed Trinity 
ultramafic-Pit River (and Mule .Mountain?) granitic 
intrusive sequence in the southeastern Klamath Moun- 
tains. 



50 



Cfology of Nortmfrn California 



Bull. 190 



The ages of regional metaniorpliism, igneous intru- 
sion, and probable thrust faulting in the Seiad Valley, 
Condre>' Mountain, and Marble Mountains areas are 
not know n, but it is difficult to separate this region 
in terms of its gross tectonic style and its mctamorphic 
and plutonic characteristics from the southeastern 
Klamath area. 

Late Jurassic orogeny in the Klamath Mountains 
appears to have been particularly pronounced in the 
western area of the province. In addition to strong 
deformation this area experienced regional metamor- 
phism (e.g., formation of the Colebrook Schist), wide- 
spread ultramafic intrusion (e.g., the Josephine pe- 
ridotite sheet), and granitic intrusion. Most of the 
granitic plutons now exposed in the Klamath province 
were probably emplaced at this time, although the full 
extent of Permo-Triassic plutonism will never be 
known in those areas where younger Triassic and 
Jurassic rocks are exposed. Late Jurassic orogenic ef- 
fects in the southeastern quarter of the province were 
apparentl\- limited to regional albitization, widespread 
granitic intrustion, and open folding. 



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mineral resources: California Div. Mines Bull. 179, 80 p. 

1963, Preliminary geologic mop of the Weaverville quadrangle, 

California: U.S. Geol. Survey Mineral Inv. Field Studies Mop MF-275, 
scale 1:62,500. 

1964, Late Mesozoic orogenies in the ultramafic belts of north- 
western California and southwestern Oregon: U.S. Geol. Survey Prof. 
Paper 501C, p. C1-C9. 

Kinkel, A. R., Jr., Hall, W. E., and Albers, J. P., 1956, Geology and 
bose-metol deposits of West Shasta copper-zinc district, Shasta 
County, California: U.S. Geol. Survey Prof. Paper 285, 156 p. 

Kistler, R. W., Botemon, P. C, and Bronnock, W. W., 1965, Isotopic 
ages of minerals from granitic rocks of the central Sierra Nevodo 
and Inyo Mountains, California: Geol. Soc. America Bull., v. 76, no. 2, 
p. 155-164. 

Kulp, J. L., 1961, Geologic time scole: Science, v. 133, no. 3459, 
p. 1105-1114. 

Lanphere, M. A., and Irwin, W. P., 1965, Isotopic age of Salmon and 
Abroms Schists, Klomoth Mountains, California [obs.]: Geol. Soc. 
America, Cordilleron Sec, 61st Ann. Mtg., Fresno 1965, p. 33. 

Lipman, P. W., 1963, Gibson Peak pluton: o discordant composite 
intrusion in the southeastern Trinity Alps, northern Californio: Geol. 
Soc America Bull., v. 74, no. 10, p. 1259-1280. 

1964, Structure and origin of an ultramafic pluton in the Klomoth 

Mountains, California; Am. Jour. Sci., v. 262, no. 2, p. 199-222. 

Merriom, C. W., 1961, Silurian and Devonion rocks of the Klomoth 
Mountains, California; U.S. Geol. Survey Prof. Poper 424-C, p. 
C188-C189. 

Moore, J. G., 1959, The quartz diorite boundary line in the western 
United States: Jour. Geology, v. 67, no. 2, p. 198-210. 

Strand, R. G., 1963, Geologic mop of California, Olaf P. Jenkins edi- 
tion. Weed sheet; California Div. Mines ond Geology, scale 1:250,000. 

Thayer, T. P., and Brown, C. E., 1964, Pre-Tertiory orogenic and plu- 
tonic intrusive activity in central and northeastern Oregon; Geol. 
Soc America Bull., v. 75, no. 12, p. 1255-1262. 

Wells, F. G., 1956, Geology of the Medford quadrangle, Oregon- 
California; U.S. Geol. Survey Geol. Quod. Mop GQ-89, scale 1:96,000. 

Wells, F. G., and others, 1940, Preliminary geologic mop of the Grants 
Pass quadrangle, Oregon: Oregon Dept. Geology and Mineral In- 
dustries, scale 1:96,000. 

Wells, F. G., and Peck, D. I., 1961, Geologic map of Oregon west of 
the 121st meridian; U.S. Geol. Survey Misc. Geol. Inv. Mop 1-325. 

Wells, F. G., and Walker, G. W., 1953, Geology of the Golice quad- 
rangle, Oregon; U.S. Geol. Survey Geol. Quod. Mop |GQ-25], 
scale 1:62,500. 

Wells, F. G., Hotz, P. E., and Cater, F. W., 1949, Preliminary descrip- 
tion of the geology of the Kerby quodrongle, Oregon; Oregon Dept. 
Geology and Mineral Industries Bull., v. 40, 23 p. 

Wells, F. G., Walker, G. W., and Merriom, C. W., 1959, Upper 
Ordovician(?) and Upper Silurian formations of the northern Klomoth 
Mountains, California; Geol. Soc America Bull., v. 70, no. 5, p. 
645-649. 



ECONOMIC DEPOSITS OF THE KLAMATH MOUNTAINS 



By John P. Albers 
U.S. Geolocicai. Survey, Menlo Park, California 



INTRODUCTION 

The metallic substances that have been produced 
from the Klamath Mountains of California (fig. 1) 
include gold, copper, zinc, pyrites, lead, silver, chro- 
mite, quicksilver, iron, platinum, and manganese. 
Limestone (for cement), sand, gravel, building stone, 
crushed rock, brick, rubble, and riprap are the im- 
portant nonmetallic products. In 1965 these non- 
metallic materials and quicksilver were the principal 
mineral products of the province. Table 1 summarizes 
the approximate total production of the major mineral 
commodities from 1880 through 1963; figures 2 and 3 
show graphically the annual production trend of these 
commodities. 




map showing location of physical features referred 



For purposes of discussion, the economic deposits 
are subdivided as follows: (1) deposits found in ul- 
tramafic igneous rocks (chromite, asbestos, and 
nickel); (2) deposits found chiefly in metamorphosed 
sedimentary and volcanic rocks, and inferred to be 
genetically related to the intrusion of granitic rocks, 
(gold, silver, copper, lead, zinc, pyrites, iron); (3) 
deposits inferred to be associated elsewhere with late 
volcanic activity (quicksilver); and (4) deposits con- 
centrated by sedimentary processes (managanese, 
placer gold and platinum, and the building materials). 

* Publication authorized by the Director, U.S. Geological Survey. 



The building materials will not be discussed in this 
paper and only brief mention will be made of placer 
deposits and manganese. Occurrences of antimony, 
arsenic, clay, graphite, molybdenite, ocher, talc, tin, 
and tungsten are also known in the Klamath Moun- 
tains, but production is negligible, and thus the occur- 
rences of these materials will not be described. 

DEPOSITS FOUND IN ULTRAMAFIC IGNEOUS ROCKS 

Chrcmiite. — Chromite has been produced from the 
Klamath Mountains only during World Wars I and II, 
when access to foreign sources was more difficult, and 
during the 1950's, when the U.S. Government pur- 
chased chromite at incentive prices for the national 
strategic mineral stockpile. At other times domestic 
chromite has been unable to compete with foreign 
sources. 



l^CuWJn 


■ 


1 


- 






1 11 


■ 


11 1 1 
ll ' ' 

11 1 1 
II II 
II II 

jii i ! 
'\ \ \ \ 




«ii 


i\n\ 


/ 




rvM' \ |; 


/ 


i. ■ 


A / ; V \i i 1 


/ 


1 1 N \ 


- i I \L 


I J 


iA^'rAA'^'i " 




1 ■<' 


y-\/\\ 



Figure 2. Production of gold, copper, lead, zinc, and pyrites be 
tween 1880 and 1963, in millions of dollars. 



[51] 



52 



Geology ok Noriiikrn California 



Bull. 190 



• nd unit ind grav«t - 




Figure 3. Production of chromite, silver, stone, sand and grovel, and 
quicksilver between 1880 and 1963, in millions of dollars. 

Because of the interest in cliromitc during World 
War II, the more important deposits in the Klamath 
.Mountains were intensi\ely studied during that period 
by the U.S. Geological Survey. The following de- 
scription is summarized largely from reports b\' Allen 
(1941); Wells, Cater, and Rynearson (1946);' Wells, 
Smith, Rynearson, and Livermore (1949); and Wells 
and Cater (1950). 

Chromite is found exclusively in ultramafic igneous 
rocks and in serpentine derived from them. The dis- 
tribution of ultramafic rocks and the location of the 
principal cliromitc deposits is shown on figure 4. The 
ultramafic rock generally forms sill-like tabular bodies 
that lie parallel to bedding or foliation in the intruded 
rocks. Individual ultramafic masses are commonlx- 
composed of more or less discrete bodies of several 
different rock t\pes — saxonite, dunite, Iherzolite, 
p>roxenite, and hornblcnditc. The chromite occurs in 
tabular or lenticular bodies of dunite that may be an\ 
size or shape and may occur anywhere within an ul- 
tramafic mass. The dunite is composed of at least 95 
percent olivine and less than 5 percent pyroxene. 

Wells and others (1949, p. 26) describe dunite in 
weathered outcrops of the eastern Klamaths as char- 
acterized by a yellowish-red color, a smooth fine- 
grained surface, protruding scattered grains of chro- 
mite or magnetite, and an irregular jointing. Unaltered 



dunite has a ragged uneven fracture, a glassy to oily 
luster, and is light \ellowish green to grayish green 
on the fresh surface. Highly serpentinized dunite, 
however, has a conchoidal fracture, a wax>' or corne- 
ous luster, and is bluish green to greenish black. Under 
the microscope, dunite shows interlocking angular 
grains of olivine from 0.5 to 1.0 mm in diameter, and 
enstatite, augite, and hornblende in minor amounts. 
Serpentine is common along cracks and cleavages and 
as rinds around olivine grains in dunite. Serpentine 
ma\' also surround chromite grains, forming an asso- 
ciation that is of great importance in crushing the ore. 

Chromite occurs in various degrees of concentra- 
tion within dunite — from tabular or podlike aggre- 
gates of almost solid chromite to deposits containing 
only a few percent of chromite as disseminated grains. 
Thus two general types of chromite deposits are rec- 
ognized: (1) pod, and (2) disseminated. The pod 
deposits consist of clean ore that can be mined, sorted, 
and shipped as lump ore. Almost all the deposits of 
Del Norte Count\- in the western Klamaths are this 
type. Ore has been shipped from about 50 pod de- 
posits which \ielded from 5 to 20,000 tons each. 
Pod deposits commonly occur in shear zones, which 
ma\' be as much as several hundred feet wide and 
several miles long. Allen (1941, p. 10.^) points out that 
elongate mas.ses of chromite may be horizontal and 
parallel to the trend of a shear zone or may be in- 
clined at any angle up to 90°. Deposits of the dis- 
seminated t\pe are composed of chromite grains scat- 
tered through dunite or serpentine derived from 
dunite. The chromite may range in concentration from 
accessor^' amounts to as much as 80 percent of the 
rock. Deposits of disseminated ore range in size from 
a few tons to more than 200,000 tons. The largest 
disseminated deposit is the Seiad Creek or Mountain 
\'iew deposit in the eastern Klamaths which accord- 
ing to Wells and others (1946, p. 33) measures 1,300 
feet long by 250 feet wide and 250 feet down dip. 
Alost of the chromite in the Klamaths, in both pod 
and disseminated deposits, is of metallurgical grade, 
with a Cr/Fe ratio of 2.50 or higher and a Cr-0:i 
content in excess of 45 percent. The richer pod de- 
posits have \ielded most of the ore to date, but ore 
reserves are mostl\' in disseminated deposits. 

Geologists who have studied the chromite deposits 
of the Klamaths generally agree that the chromite w^as 
formed s\ngcneticall\' with the enclosing ultramafic 
rock, .\llcn (1941, p. 103), in discussing chromite in 
California, states that most of the chromite bodies 
were emplaced late in the magmatic c\ cle, in some 
cases while differentiation was still g<iing on. Wells 
and others ( 1949, p. 34), on the basis of detailed 
studies of structures in the ore and studies of internal 
structures of the enclosing ultramafic rock masses in 
the Seiad \'alle\-.McGuff>' Creek area, conclude that 
the chromite w as as truly a component of the original 
ultramafic magma as the olivine and pyroxene. In their 
view the chromite crystallized early and accumulated 



1966 



Albers: Klamath Mountains 



53 




EX PLANATION 
Cretaceous sad younger rock 



Granitic rocks 



C: ProductiTe chroaite deposit 
or group of deposits 

Q: Quicksi Iver deposit 
A: Asbestos occurrence 



Ultraaafic rocks 



Paleozoic and Mesozoic 
net a sedimentary and 
netavolcanic rocks 

Figure 4. Distribution of chromite, asbestos, and quicksilver deposits in the Klamath Mountains of 
California. 



54 



Geology of Northern California 



Bull. 190 



Table I. Approximate I'alue of principal mineral coiimiodities 
prodttced in the Klamath Mountains from 1880 through 1963 



Commodity 



Gold ... 

Copper, lead, and zinc 
Miscellaneous stone'.. 

Pyrites* 

Silver 

Chromite 

Mercury' 

Platinum 

Total 



i514O,127,320 

139,503,044 

42,030,009 

21,178,850 

13,046,907 

8,975,260 

1,310,796 

185,830 



^366,358,016 



(Data from U.S. Bureau of Mines Mineral Yearbooks and California 

Di\ision of Mines and Gcolog>' publications.) 
' Includes sand and gravel; excludes brick and cement. 
* Data in part from \lountain Copper Company of California. 
' Trinity- County only. 

in certain zones within the melt to form chromite-rich 
la\ers and bodies. The\' also think that cnstallization 
of most of the chromite, much of the olivine, and 
some of the p\ro.\ene was completed when the cr\stal- 
bearing mush moved from its cr>stallization chamber 
into its present position. 

Because chromite is s>ngenetic with ultramafic rock, 
which was emplaced before the granitic rocks with 
which most of the epigenetic mineral deposits are be- 
lieved to be related, it is inferred that the chromite 
ore bodies represent the oldest mineral deposits in the 
Klamath Mountains. 

Asbestos. — Occurrences of asbe.stos are fairly nu- 
merous in the Klamath Mountains but the quantity 
mined to date is insignificant. Nearly all occurrences 
are in serpentine derived from peridotite (fig. 4). Two 
types of asbestos are found: (1) chrysotile or cross- 
fiber asbestos; and (2) amphibole (tremolite) or slip- 
fiber asbestos. Chrysotile has the higher tensile 
strength and therefore has a higher value. The chrxso- 
tile deposits commonly consist of a small zone of 
closely spaced veins that range in thickness from a 
fraction of an inch to about an inch. The fibers are 
oriented at right angles to the vein walls. The amphi- 
bole asbestos veins, on the other hand, are commonly 
along shear zones a few inches wide and have fibers 
oriented more or less parallel to vein walls. In a few- 
places the amphibole veins contain lenticular pockets 
of fiber several feet wide. Rice (1957) describes a 
vein at the Sylvester mine, in Shasta County, which 
had a ma.ximum uidth of 30 inches and was mined 
over a length of at least 110 feet. Owing to a limited 
market and the expense of handling, few amphibole 
veins are worked to depths greater than 25 feet. It 
appears that a successful amphibole asbestos industry 
in the Klamaths would depend on the discovery of 
deposits having a minimum strike length of several 
hundred feet. 

Although the spatial relationship of both chrysotile 
and amphibole asbestos deposits to serpentine is clear, 
the genetic relationship is uncertain. The occurrence 



of asbestos in veins and shear zones indicates an epi- 
genetic origin, possibly related to the process of ser- 
pentinization or to the intrusion of granitic rocks. 

Nickel. — Ferruginous nickeliferous lateritic soils — 
formed by weathering of ultramafic rocks in place — 
are rather widespread in the Klamath .Mountains but 
no production has \et been realized. Hotz ( 1964) be- 
lieved that the soils were formed by chemical weather- 
ing in a climate characterized by alternate wet and dry 
seasons — similar to that prevailing today. The most 
likel\' time of their formation is post-Miocene to Pleis- 
tocene. Because the deposits are small, are low grade, 
and have a scattered distribution in a rugged and rela- 
tively isolated terrain, they are unlikel\- to be exploited 
in the foreseeable future. 

DEPOSITS CHIEFLY IN METAMORPHOSED SEDIMENTARY AND 

VOLCANIC ROCKS AND INFERRED TO BE GENETICALLY 

RELATED TO GRANITIC ROCKS 

Gohi. — Gold ranks as the principal mineral product 
of the Klamath Mountains. Approximately $140 mil- 
lion worth of gold has been produced since 1880 
(table 1); in addition at least several million dollars 
worth was mined between 1848 and 1880. 

As shown by figure 1, gold production reached an 
early peak of about $3 million in 1894 and then de- 
clined irregularly to less than |1 million annually 
during the I920"s. Then, in the 1930's, stimulated by 
the Great Depression which drove man\- people into 
prospecting, and by a substantial rise in price from 
$20.67 to $35.00 a fine ounce in 1934, production rose 
sharply and reached a peak of about $5.5 million in 
1941. World War II resulted in a very sharp decline; 
since 1943 production has averaged well under $1 mil- 
lion a year. 

The gold has come from three main sources: (1) 
placer deposits; (2) lode deposits; and (3) as a by- 
product of massive sulfide deposits mined chiefl\- for 
their copper content, and from gossan derived from 
massive sulfide. About $12 million of the $140 million 
total has come from massive sulfides. Of the remaining 
$128 million, about 70 percent has come from placer 
deposits, and the remainder from lode deposits (Irwin, 
1960, p. 64). 

During the first few years after its discovery in 1848 
gold was produced mainly from placer deposits. The 
first lode mining began at the Washington mine (fig. 
5) in 1852, but for many years the output of lodes 
was far below that of the rich gulches and bench 
gravels (Ferguson, 1914, p. 33). Lode mining increased 
in relative importance in the 1880's and probably 
yielded at least as much gold as placer mining until 
World War I. During the 1930's the great bulk of the 
gold produced was from dredging operatioiis. Fine- 
ness of gold in the Klamaths has averaged about 850. 

Placer deposits are located mainly along the Trinity 
and Klamath Rivers and their tributaries and along 
Clear Creek. Pleistocene gravels and gravels of the 
Tertiary Weaverville Formation have also yielded sig- 



1966 



Albers: Klamath Mountains 



55 




EX PLAHATIIN 



Cretaccoaa tmi yemm$tT rocks 
Graaitic rocks 
Ultrasafic rock* 



Paleoxoic and Mesoioic 

■etasediaentary and 

■ctaTolcanic rocks 



Base netal deposit, chiefly 
nassiTC sulfide containing 
copper, lead, tine, pyrite, 
gold, and silver; includes 
sone disseainated and 
»ein types 



LIST OF MINES AND DEPOSITS REFERRED TO IN THE TEXT 



GOLD MINES 

1. Washington 

2. Alaska 

3. Black Bear 

4. Brown Bear 

5. Gilta 

6. Gladstone 

7. Hazel 

8. Klamath 

9. Golden Eagle (Sheba) 

10. Fairview 

11. Five Pines 

12. Venecia 



13. Dewey 

14. Headlight 

15. Cummings (Oro Grande) 

16. Highland I 

17. Midas (Harrison Gulch) 

18. Trinity Bonanza King 

IRON DEPOSITS 

19. Shasta 

20. Hirz Mountain 
BASE METAL DEPOSITS 

21. Blue Ledge 

MANGANESE MINE 

34. Shasta Copper mine 



22. Gray Eagle 

23. Copper Bluff 

24. Iron Mountain 

25. Keystone and Balaklala 

26. Shasta King 

27. Early Bird 

28. Mammoth 

29. Sutro 

30. Bully Hill Rising Star 

31. Afterthought 

32. Greenhorn 

SILVER MINE 

33. Silver Falls -Consolidated 



Figure 5. Distribution of gold lodes, iron, base metal, silver, and manganese deposits in the Klamath Mountains of Colifori 



56 



Gkolooy of Northk.rn California 



Bull. 190 



nificant amounts of gold. The gold in all these placer 
deposits was derived from eroded segments of the lode 
deposits described below. 

No overall study of the lode deposits of the Klamath 
Mountains has been made. However, geologists of the 
U.S. Geological Survey (MacDnnald, 1913; Fergu.son, 
1914; and Albers, 1961, 1964) have studied individual 
districts and groups of districts, and geologists and 
engineers of the California Division of Mines and Ge- 
ology have reported on the geology of individual 
mines, mainly on a county basis (Brown, 1916; Averill, 
1931, 1933, 1935, 1941). The summary description of 
the principal kinds of deposits given below is based 
partly on these writings and parth' on the writer's 
knowledge of the region. 

Figure 5 shows that most of the principal lode de- 
posits lie in an arcuate belt that parallels the gross 
structural grain in the central part of the Klamaths. 
They are predominantly in weakh' metamorphosed 
sedimentary- and volcanic rocks of Paleozoic age, and 
the great majority arc closely associated with dike-like 
or sill-like bodies of a porphyry known by local 
miners as "birdseye" porphyry. This porphyry differs 
somewhat in composition from place to place and in- 
cludes two principal rock types — diorite porphyry and 
dacite porphyry. Overall, the "birdseye" porphyry 
bears a strong affinir\' to the quartz diorite and grano- 
diorite plutonic rocks of the Klamath Mountains and 
appears to be genetically related to the plutons. In 
addition to the "birdseye" porphyry, dikes of quartz 
porpayr>- are commonly associated with gold lodes in 
the southeastern part of the region. 

The principal lode deposits are veins that occur in 
the following geologic environments: ( 1 ) steeply dip- 
ping veins in black carbonaceous shale or slate (Alaska, 
Black Bear, Brown Bear, Gilta, Gladstone, Hazel, and 
Klamath deposits are examples); (2) steeply dipping 
veins in greenstone that underlies shale or slate in much 
of the region (Golden Eagle, formerly Sheba, de- 
posit); (3) gently dipping veinlike deposits along 
faulted contacts between shale and greenstone (Fair- 
view, Five Pines, Venecia, and Washington deposits); 
(4) steeply or gently dipping veins in "birdseye" por- 
phyry dikes or quartz porphyry dikes (Dewej' and 
Headlight deposits); and (5) steeply dipping dikes in 
schists and miscellaneous rock types (Cummings, for- 
merly Oro Grande, Highland I, Midas, and Trinity 
Bonanza King deposits). 

Several of the five tj'pes of deposits may be found 
within an individual district. Such a district is the 
French Gulch-Deadwood district, which has yielded 
at least 800,000 ounces of gold. It contains some of 
the largest producing mines representing at least three 
of the five types of deposits. The district lies about 20 
miles northwest of Redding in the southern part of 
the region and is in an eastward-trending highly frac- 
tured belt about 9 miles long and a mile wide. It in- 
cludes the Brown Bear mine at its western end and 



the Gladstone luine at its eastern end (fig. 5). The 
rocks arc chiefly shaly rocks of the Mississippian Brag- 
don Formation and the underlying Dcvonian(?) Cop- 
lex (Irccnstonc, u hich delineates an eastward-trending 
archlike structure just north of the fractured belt 
(Albers, 1961, p. Cl). The contact between the Brag- 
don and Copley Formations is structurally discordant 
and is interpreted as a low-angle thrust fault that has 
been disrupted bv later high-angle faulting (.■Mbers, 
1964, p. J62). 

The Shasta Bally batholith of silicic quartz diorite 
and granodioritc intrudes the Bragdon and Coplc\- 
Formations about a mile west of the French Ciulch- 
Dcadwood district. In the western part of the district 
numerous "birdseye" porpli\r\- dikes intrude tiic Brag- 
don Formation and locally form sill-like bodies along 
the contact between the Bragdon and Copley. One 
group of these dikes is similar in composition to the 
Shasta Ball\ batholith, and at least one dike is also 
similar in texture. Because of the similarit\' the dikes 
are regarded as offshoots from the batholith, and a 
salient of the batholith is inferred to extend in an 
easterly direction beneath the fractured, intruded, and 
mineralized belt (.'\lbers, 1961, p. C2). .Most fractures 
trend parallel to the belt and are thought to he at 
least in part tension fractures formed by the upward 
push of the magma of the salient. Subscqucntlv, man\' 
of the fractures controlled the emplacement of "birds- 
eye" porph\ry dikes and quartz veins. 

The t\pes of lodes in the French Gulch-Deadwood 
district include: ( 1 ) steeph' dipping quartz and quartz- 
calcite veins in shaly rocks of the Bragdon Formation; 
( 2 ) gentl\- to moderatelv dipping quartz and quartz- 
calcite veins along the thrust contact between the 
Bragdon and Coplc\' Formations; and ( 3 ) veins in the 
"birdseye" porphyry dikes and sills. In addition, a 
fourth t\pc of deposit — steeplx" dipping quartz veins 
in greenstone — occurs in at least one mine in the dis- 
trict (Washington) but has accounted for very little 
production. 

.Most gold has come from the stccpl\ dipping veins 
in the Bragdon Formation. Workings of the two larg- 
est mines — Brown Bear and Gladstone — as well as sev- 
eral other mines, are on such veins, and although some 
workings are more than 1,000 feet deep the\' have not 
penetrated the Copley Greenstone contact. On the 
other hand, most gold from the intervening Washing- 
ton mine (fig. 5) has come from lodes along the con- 
tact between the Bragdon and Copley Formations. 
The "birdseye" porphyry dikes and sills that arc abun- 
dant in the Brown Bear and other mines of the western 
part of the district are in many places cut b\- gold- 
bearing quartz veins. Quartz porph\r\- dikes and sills 
— the soda granite porphyry of Ferguson (1914) — are 
also common in the western part of the district. No 
"birdseye" porphyry is known in the mines of the 
eastern part of the district but some quartz porphyry 
has been reported in the Gladstone mine. 



1966 



Albkrs: Ki.a.math Mountains 



57 



The ore shoots in the steeply dipping veins ;it the 
Brown Bear and other mines in the district are com- 
monly at the intersection of veins which have opposing 
dips or at the intersection of veins \\ ith contacts l)e- 
tween shale and porphyry. The two principal veins at 
the Brown Bear mine are essentiall\' parallel in strike 
but intersect in places because of variable and opposing 
dips. Subsidiary veins also intersect the main veins. 
Nearly horizontal ore shoots are thus formed along 
the line of intersection at rvvo main levels in the mine. 
In contrast to the highly productive, steeply dipping 
\'eins in the Bragdon Formation, similar steep veins in 
the Copley Greenstone, as in the deeper le\els of the 
Washington mine, are commonly narrow and of poor 
grade; only at the contact \\ith the shale of the Brag- 
don are they productive. 

Much of the richest gold ore within the Bragdon 
was reportedly along contacts between the quartz 
veins and black slickensided graphitic shale, or asso- 
ciated \\ith inclusions of graphitic shale in the vein, 
suggesting the importance of graphitic material as a 
precipitating agent for gold. This importance of car- 
bon or graphite as a precipitating agent has been noted 
by Hershey (1910) and Ferguson (1914, p. 40-43). 
Ferguson thought that the pocket gold deposits of 
the Klamath Mountains, found mainly at the contact 
between the Copley and Bragdon Formations, were 
of surficial origin, formed as a result of precipitation 
of gold from surficial waters where these waters first 
came in contact with graphitic material of the Brag- 
don. According to this interpretation the gold was 
taken into solution by surface waters from p\'ritized 
zones in greenstone in the presence of manganese 
o.xide. Although this may be a valid hypothesis for 
the origin of some pockets, it seems to the writer that 
to be effective the depositional process would require 
ascending surficial solutions, inasmuch as the shaly 
rocks overlie the greenstone. A preferred interpreta- 
tion is that the gold was deposited by rising h\dro- 
thermal solutions at and above the contact between 
greenstone and overlying shaly rocks. By this inter- 
pretation the gold in steeply dipping veins within the 
Bragdon, or in veins cutting "birdse\e" porph\'r\' 
dikes in the Bragdon, represents a residue in solutions 
that must have come past the more favorable contact 
between Copley and Bragdon. Therefore the possi- 
bility that additional ore will be found at depth in 
mines such as the Brown Bear and Gladstone that 
have not penetrated as deep as the Cople\- Greenstone 
appears promising. 

The mineral composition of veins shows little varia- 
tion. Quartz is the chief gangue mineral, calcite and 
mica are present in minor amounts, and locally man- 
ganese oxide occurs near the surface. Pyrite, galena, 
sphalerite, arsenopyrite, and less common chalcopyrite 
are the sulfides. Gold occurs mainly as free gold but 
also occurs in the sulfide minerals. 



If the inference that the porphyry dike rocks in the 
western part of the French Gulch-Deadwood district 
are offshoots from an underlying salient of the Shasta 
Bally batholith is correct, it appears highly probable 
that the gold-bearing quartz veins originated from the 
same magmatic source. The veins are apparently con- 
trolled by the same eastward-trending fracture system 
that controls the dikes, and are at least slightl\- 
\ ounger than the dikes. The veins are interpreted as 
residual fluids rising from the cooling batholith salient 
along reopened fractures of the same system that had 
previousl)' gixen access to the dikes. As the veins 
traversed the Copley Greenstone little gold was de- 
posited except in small pockets, but where the solu- 
tions encountered graphitic material at and above the 
Copley-Bragdon contact, gold was precipitated, par- 
ticularl)' at the intersections of fractures where gra- 
phitic material w as abundant. 

Elsewhere in the Klamath Alountains many of the 
best gold mines are in a geologic environment grossly 
similar to that of the French Gulch district. However, 
a few gold lodes are in schistose rocks, as the .Midas 
(Harrison Gulch) deposit in the extreme southern part 
of the region, and the Bonanza King deposit in the 
east-central part (fig. 5). As in the French Gulch- 
Deadwood district, the principal ore is free gold in 
quartz or quartz-calcite veins. Tellurides are reported 
in a few localities. 

"Birdse\'e" porph\ry dikes are associated with many 
but not all the deposits throughout the Klamath 
Mountains. The importance of the "birdseye" por- 
phyry dikes was recognized by MacDonald (1913, p. 
19), who, in discussing the Carrville district of the 
central Klamath Mountains, advised prospectors to 
search all contacts of "birdseye" porphyry dikes. The 
close association between gold lodes and porphyry- 
dikes in so many localities strongl\' suggests a genetic 
relationship. It seems equalh- clear that the "birdseye" 
porphyry dikes are offshoots from large plutonic 
bodies as previously described in the French Gulch- 
Deadwood district. Probabh' the gold-bearing quartz 
and quartz-calcite veins came from the same magmatic 
source and followed ver\' nearly the same fracture 
s\'stems as the dikes. 

The outcrop pattern (fig. 5) suggests that silicic 
plutonic rocks may lie at relatively shallow depth 
beneath much of the eastern part of the Klamaths 
where most of the gold lodes occur. Therefore those 
lodes that have no associated "birdseye" porphyry dikes 
may have been derived from plutonic rocks at depth. 
The onl\- condition nccessar\' for their formation was 
a fracture system allowing access of mineralizing 
fluids from the plutonic bodies to the host rocks. 

Iron. — Onl\^ two iron ore deposits of economic 
significance are known in the Klamath .Mountains 
province. These are the Shasta and Hirz Mountain de- 
posits along the McCloud River arm of Shasta Lake a 
few miles north of Redding (fig. 5). Iron ore was pro- 
duced on a small scale from the Shasta deposit inter- 



5g 



CiKOUKiY OK NORTHKRN CALIFORNIA 



Hull. !';() 



TRINITY 



ALPS 



>lTOSta oa 



Highway 





Keswick Dam 




Groundi ' 





Pholo 1. Aerial photo of Redding and the Trinity Alps. 



mittentiy between 1907 and 1926, and several hundred 
thousand tons were mined during the period 1942-1944 
for use as ballast by the U.S. Navy. No production has 
been realized from the Hirz Mountain deposit. Both 
deposits are contact metasomatic replacement deposits 
localized along contacts between the Permian Mc- 
Cloud and Nosoni Formations and an irregular large 
dikclike body of quartz dioritc. The ore occurs as a 
replacement of the .McCloud and Nosoni Formations 
and also as a replacement of the quartz dioritc. It con- 
sists chiefl\' of magnetite accompanied by garnet and 
epidote. For a more complete description of these 
deposits the reader may refer to Lamev (1948a. 
1948b). 

Massive sulfides and replaceviein veins. — The base 
metals, particularl\- copper, and to a much lesser ex- 
tent zinc and lead, rank with gold as the chief mineral 
products of the Klamath Mountains (table 1), and 
well over 90 percent of these base metals have come 
from massive sulfide deposits of the West Shasta and 



East Shasta copper-zinc districts in the eastern part of 
the region. The remaining base-metal production is 
mainl\- from the Blue Ledge and Gra>' F.agle replace- 
ment vein deposits near the Oregon border, and the 
Copper Bluff deposit in the western part of the 
province. 

The first massive sulfide deposits were discovered 
in the 1860's, and during the early years their oxidized 
outcrops were worked for precious metal content. 
Beginning in 1896 and for more than 20 \cars there- 
after, the unoxidized sulfide ore was exploited, and a 
large mining industry- grew up in the area north of 
Redding. The massive sulfides were direct smelted 
during most of this period, and copper along with 
some gold and silver were the onl\- metals recovered. 
Zinc was successfully recovered from some ores in 
1918, and thereafter was an important product of the 
district. Lead production has been relatively insignif- 
icant. 



1966 



Albers: Klamath Mountains 



59 



As shown in figure 2, the production of base metals 
reached a high of 111 million (nearly all from copper) 
in 1917 and declined sharply to virtually nothing in 
1920. During the 1930's about 2.6 million tons of 
gossan derived from oxidation of massive sulfide at the 
Iron Mountain deposit (fig. 5) was treated for its gold 
content, and from 1948 until 1962 the same deposit 
yielded pyrite from which sulfur was extracted for 
use in making sulfuric acid. In all, the Iron Mountain 
mine in the West Shasta district was a continuous 
producer of mineral products for a period of more 
than 65 years, and it (as well as the other massive sul- 
fide mines) was of prime importance in the economic 
development of northern California. 

Important deposits in addition to Iron Mountain are 
the Mammoth, Balaklala, Keystone, Earl\- Bird, Shasta 
King, and Sutro (fig. 5); these make up the West 
Shasta copper-zinc district which has yielded the bulk 
of the production. The Bully Hill-Rising Star and 
Afterthought mines make up the East Shasta copper- 
zinc district (fig. 5). Both districts have been studied 
in detail in recent \ears by the U.S. Geological Survey 
(Kinkel, Hall, and Albers, 1956; Albers and Robert- 
son, 1961). The Greenhorn mine is another fairly 
large massive sulfide deposit that lies a few miles west 
of the West Shasta district. 

The massive sulfide deposits of the West Shasta 
copper-zinc district lie in a belt about 9 miles long, 
I mile wide and trending N. 25° E. All the deposits 
are in an altered silicic volcanic rock unit of Devonian 
age called the Balaklala Rh\olite. The deposits lie at a 
more or less consistent stratigraphic position within 
the formation, beneath a layer of pyroclastic rocks in 
some places, and in other places beneath a coarseh' 
porphyritic facies of rhyolite that is the stratigraphic 
equivalent of the p\'roclastic beds. The massive sulfide 
bodies are mainl\' lenses, pods, or cigar-shaped masses. 
They are in sharp contact with wallrocks which are 
everywhere altered and more or less pyritized. The 
length and width of massive sulfide bodies are com- 
monly 2 to 10 times the thickness, and except at the 
extreme north end of the district the long axes of the 
sulfide bodies are essentially horizontal. The bodies 
range in size from a few thousand tons to more than 
5 million tons. However, the several discrete bodies 
mined at Iron Mountain were, before faulting and ero- 
sion, a continuous mass about 4,500 feet long and con- 
taining perhaps 25 million tons of massive sulfide. 

Although the sulfide bodies are everywhere in sharp 
contact with the wallrocks, the contacts are not frozen. 
Typically, a thin seam of gouge separates massive 
sulfide from wallrock. In many localities the evidence 
is clear that the sulfide has replaced the enclosing host 
rocks. A fault set striking about N. yO'' E. across the 
N. 25° E. grain of the district is older than the min- 
eralization and probably provided the main feeder 
channels for the sulfide ore. All the ore bodies are 
near these faults but not all are adjacent to them. Some 



ore bodies in the West Shasta district are on or near 
the axes of folds in the host rock, but there seems to 
be no preference for anticlines or synclines; in any 
case not all sulfide bodies show a preference for folds. 

The massive sulfide ore is typically 90 to 95 per- 
cent sulfide minerals — dominantly p\rite, with lesser 
amf)unts of chaicopxritc, sphalerite, quartz, and calcite. 
The ore has a brassy appearance and is generally struc- 
tureless. The average grain size is about half a milli- 
meter, but locally it is much coarser. Much of the 
massive sulfide is essentially p\rite that contains very 
little chalcopyrite or sphalerite. This low-grade copper 
ore has been mined at Iron Mountain for its sulfur, 
but elsewhere in the district it has been treated as 
waste during mining operations. The low-grade mas- 
sive pyrite occurs as separate bodies and also as parts 
of ore bodies that contain copper and zinc values high 
enough to be mined as base-metal ore. The copper 
content of ore mined for copper ranged from 2 to 
7.5 percent. Zinc content ranged as high as 21.1 per- 
cent in parts of the Mammoth mine, but the content 
of this metal is extremely variable and would probably 
average well under 5 percent in the base-metal ore 
mined throughout the district. No lead is present in 
the West Shasta sulfide ores, but most of the ore con- 
tained 0.02 to 0.06 ounce of gold and 1 to 8 ounces 
of silver per ton. 

Kinkel, Hall, and Albers (1956, p. 93), as well as 
other geologists who have worked in the West Shasta 
district, believe that the massive sulfide deposits formed 
by replacement of the Balaklala Rhxolite. Perhaps the 
most convincing evidence for this is the presence in 
a few places of relict quartz phenocrysts of the re- 
placed host rock in the massive sulfide ore. Other 
evidence in the sulfide is local banding, which is prob- 
ably inherited from foliation in the enveloping host 
rock. Also, the abundant disseminated pyrite that oc- 
curs throughout the district is clearly replacement in 
origin. The ore controls in summar\- are: ( 1 ) favor- 
able stratigraphic position in the Balaklala Rhyolite; 
(2) the N. 70° E. trending premineralization feeder 
faults; and (3) in local areas, secondary foliation in 
the host rock. The deposits are probabl\- late Jurassic 
or possibly very early Cretaceous in age. 

The source of the solutions that deposited the mas- 
sive sulfides is unknown. However, the district lies 
at the north end of a large .stock of altered quartz 
diorite (fig. 5) and only a few miles from the Shasta 
Bally batholith. Either of these bodies may continue 
at depth beneath the West Shasta district and either 
could have supplied the mineralizing fluids. The me- 
tallic constituents could have come from the plutonic 
masses themselves or could have been derived in large 
part from the Copley Greenstone that lies at depth 
beneath the mineralized belt. Computations based on 
spectrographic analyses indicate that the Copley 
Greenstone and rocks of similar character in the stra- 
tigraphic section contain roughly 1 million tons of 



60 



Gf.ology of Norihern California 



Bull. 190 



metallic copper and over 2 million tons of metallic 
zinc per cubic mile. These rocks are strongly and per- 
vasively altered, and large amounts of material have 
been added and removed by metasomatic processes. 
Probably at least 5 to 10 cubic miles of greenstone lie 
directly beneath the West Shasta district; only a small 
percentage of their copper and zinc need to have 
migrated from the greenstone and been concentrated 
in the sulfide deposits to acccjunt for the 340,000 tons 
of copper and 30,000 tons of zinc that the ore bodies 
have yielded. 

The speculations in the preceding paragraph apply 
if — as the availal)lc evidence seems to indicate — the 
deposits are strictl)' epigenetic. However, the evidence 
for epigenetic origin is not conclusive, and the idea 
that massive sulfide deposits of this type may be s\'n- 
genetic is gaining favor among some geologists. It is 
possible that the sulfides were precipitated in a sub- 
marine environment in stagnant waters heavily laden 
with metallic e.xhalations from a nearby volcanic 
source. Such a syngenetic origin, however, would 
seem to require some redistribution of the sulfides 
during a subsequent orogeny to account for the epi- 
genetic relationships observed. 

The massive sulfide deposits in the East Shasta 
copper-zinc district are much smaller than those in 
the West Shasta district and have yielded only about 
15 percent as much base metal — about 30.000 tons of 
copper and 25,000 tons of zinc. The assay of mined 
ore averages about 15 to 20 percent zinc, 3 percent 
copper, to 2 percent lead, 5 ounces silver, and 0.03 
ounce gold per ton. The deposits occur as lenses that 
replace two rock units of Triassic age — an altered 
silicic volcanic rock unit called the Bully Hill Rhyo- 
lite, and the Pit Formation consisting of shale and tuff. 
Most of the sulfide lenses are tabular and steeply in- 
clined. A few are cigar shaped. They range in size 
from a few inches to as much as 400 feet in greatest 
dimension. The largest lenses have a maximum thick- 
ness of 35 to 40 feet. Most lenses are clearly controlled 
by shear zones, and they lie generally parallel to 
schistosity or bedding in the host rocks. Their walls 
are either frozen to the country rock or are separated 
from it by a layer of cla^'ey gouge. The walls of most 
sulfide lenses are sharp and smooth, but the edges, in 
contrast, are commonly irregular. Some lenses taper 
to a knife edge. Others pinch out in many thin layers 
or sheets e.xtending a few inches to a few feet into the 
host rock. Much of the sulfide ore is banded, and in 
places near the edges of lenses the banding parallels 
bedding or schistosity in the host rock. Both the band- 
ing and the presence of structurally oriented horsts 
of country rock enclosed in sulfide lenses are con- 
vincing evidence of a replacement origin for the sul- 
fide. 

Much of the sulfide ore is fine grained; it consists of 
intimate mixtures of pyrite, sphalerite, chalcopyrite, 
galena, and tetrahedrite-tennantite. Quartz, barite, 



calcite, anhydrite, and g\psum are the principal gangue 
minerals. In general the proportion of gangue minerals 
to sulfides is apprcciabl\ higher than in the West 
Shasta deposits, and the proportion of pyrite to other 
sulfide is much lower. The problem of the origin of 
mineralizing solutions and the source of the base metals 
is esscntiall\- the same as in the West Shasta district. 
The closest plutonic rock outcrops are two small stocks 
of altered (juartz diorite about 5 miles awa\- on either 
side of tiic deposits, but possibly these stocks are 
merel\' eminences rising from a subjacent mass con- 
cealed at a depth of a few thousand feet beneath the 
deposits. 

The occurrence of massive sulfide deposits in forma- 
tions of vastly different age (Devonian and Triassic) 
within the restricted area of the West and F.ast Shasta 
copper-zinc districts is additional strong evidence fa- 
voring an epigenetic origin for both the West and East 
Shasta deposits. It is highly improbable that identical 
conditions conducive to the formation of syngenetic 
massive sulfides had been repeated in an area with such 
an active tectonic and depositional historv. 

The Blue Ledge mine, near the California-Oregon 
border (fig. 5), has yielded about 11,151 tons of ore 
containing 12.12 percent copper, 0.092 ounce of gold, 
and 5.24 ounces of silver per ton (Hundhausen, 1947, 
p. 5). Most of the production was during World War 
I. The deposit is a replacement vein that dips about 60^ 
W. in quartz-muscovite schist, .\lthough the deposit 
consists of fairl)' massive sulfide (p)rite, p\rrhotite, 
chalcopyrite, and sphalerite), it is not strictly the mas- 
sive sulfide type of deposit because of its veinlike form. 
The vein is 1,300 feet long. 5 feet thick, and has been 
followed to a depth of 350 feet. 

A second deposit with production of some signifi- 
cance in the northern part of the area is the Gra\ 
Eagle mine (fig. 5). According to Brown (1916, p. 
818), this deposit is a vein 10 to 80 feet thick that 
strikes northwest and dips 45° northeast, .^n ore shoot 
over 300 feet long consists of chalcop\rite and p\rite. 
The ore carries from 2.5 to 18 percent copper and 
1 1.50 per ton in gold. The surface outcrop is marked 
by a gossan. 

The Copper Bluff deposit in the western Klamaths 
(fig. 5) is a licdded replacement deposit in chlorite 
schist beneath a black carbonaceous phyllite (H. K. 
Stager, written communication, 1959). The ore has 
an average thickness of 5 feet. During the 1950's about 
10,000 tons of ore milled had an axerage gross value 
of $6.50 per ton. Silicic plutonic rocks crop out no 
closer than 4 or 5 miles from anv of the three deposits 
mentioned above. Hence there ma\' or may not be a 
genetic relation between these deposits and the em- 
placement of plutonic rocks. 

Silver. — ."Vbout $ 1 3 million worth of silver has been 
recovered from ore mined in the Klamath Moun- 
tains. Most of this ore v\as produced from the massive 



1966 



Albers: Klamath Mountains 



61 



sulfide deposits in the West and East Shasta copper- 
zinc districts. 

The only silver mine of any consequence is the 
Silver Falls-Consolidated mine about 12 miles south- 
west of Redding (fig. 5). This mine was discovered 
about 1866, and most of its production was achieved 
prior to 1900. \"eins striking N. 45° E. to N. 60'" E. 
are from 10 inches to 2 feet wide and dip steeply. 
The veins are in quartz diorite of the Shasta Bally 
batholith. According to Tucker (1923, p. 313) the 
silver-bearing mineral is tetrahedrite, associated with 
galena, pyrite, sphalerite, chalcopyrite, and gold. A 
few other silver-bearing veins near the Silver Falls- 
Consolidated deposit are also known. 

All are along fractures in the Shasta Balh- batholith 
and are inferred to be geneticallv related to the batho- 
lith. 

DEPOSITS INFERRED TO BE ASSOCIATED 
WITH LATE VOLCANIC ACTIVITY 

Quicksilver. — Occurrences of quicksilver are found 
at several \\idely scattered localities in the Klamath 
iMountains, but the only deposit having significant 
production is the Altoona mine in the east-central part 
of the area (fig. 4). This deposit, discovered in 1871, 
has a recorded production of about 34,000 flasks, 
mostly recovered prior to 1900, and significant re- 
serves of good grade ore reportedly still remain. The 
geology of the deposit has been reported on by Swin- 
ney (1950). More recently the deposit was explored 
under a Defense Minerals Exploration Administration 
contract, and much of the material below is taken 
from H. K. Stager (written communication, 1958), 
who studied the geology in connection with the ex- 
ploration work. 

The ore bodies are along steeply dipping shear zones 
up to 30 feet wide that cut altered porphyritic diorite 
and serpentinized peridotite. The ore bodies are found 
only in diorite. They are tabular lenses that average 
5 feet thick and are as much as 270 feet long and 
extend down dip as much as 300 feet. The diorite host 
is intensely altered and replaced by quartz and car- 
bonates. The resulting rock resembles the silica-car- 
bonate rock of Coast Range quicksilver deposits. Ore 
minerals are cinnabar and native mercury. The cinna- 
bar is in small crystals disseminated in the sheared and 
altered diorite and as veinlets and fracture coatings. 
Native mercur\' is common in vugs and cinnabar- 
lined cavities in the rock, and some vugs have yielded 
as much as several pounds of native mercury. Gangue 
minerals are ankerite, pyrite, barite, quartz, and clay 
minerals. The two main types of ore are an altered 
diorite type and a carbonate type. Although both 
types may be found in the same shear zone, most of 
the production has come from the diorite type. 

Of the several other localities in the Klamath Moun- 
tains where quicksilver is known to occur (see Irwin, 
1960, p. 72) one of the most promising is the Webb 
deposit in the extreme northwestern part of the area. 
According to Cater and Wells (1953) this deposit is 



on a shear zone in serpentinized saxonite intruded by 
small irregular bodies of diorite and by felsite dikes. 
Production has been very small. 

The age and genesis of quicksilver deposits in the 
Klamath Mountains cannot be directl\- determined 
from the observed relations. The quicksilver deposits 
in the California Coast Ranges to the west and south 
are generally regarded as post-Miocene in age and are 
genetically related to late Tertiary or Quaternary vol- 
canism. However, there are no known volcanic cen- 
ters near the Klamath Mountains deposits. 

DEPOSITS CONCENTRATED BY SEDIMENTARY PROCESSES 

The mineral commodities geneticall\- associated with 
sedimentary processes include placer gold and plati- 
num, building materials, and manganese. Placer gold, 
important historically, has been di.scussed earlier; plati- 
num was produced from placer deposits intermittently. 
Stone and sand and gravel are important economic 
commodities, as shown by figure 3, but the occurrence 
of mineable deposits will not be discussed here as it 
depends more on economic factors than on geologic 
relations. 

Ma7iganese. — Although numerous occurrences of 
manganese are known in the area, production has been 
negligible. A small production has come mostly from 
the Shasta Copper mine (fig. 5) where about 1,000 
tons of ore containing 27 percent manganese was pro- 
duced. Most of the deposits are associated with bedded 
chert in greenstone or schist. The primary manganese 
mineral is the silicate rhodonite, which cannot under 
present technologic conditions be utilized as ore, and 
which oxidizes slowly, \ielding only small shallow 
pockets of manganese oxide. The individual manga- 
nese deposits are described by Trask and others ( 1950). 



REFERENCES 

Albers, J. P., 1961, Gold deposits in the French GulchDeadwood 

district, Shasta and Trinity Counties, California: U.S. Geol. Survey 

Prof. Paper 424-C, art. 147, p. C1-C4. 
1964, Geology of the French Gulch quadrangle, Shasta and Trinity 

Counties, California: U.S. Geol. Survey Bull. 1141-J, p. J1-J70. 
196 , Economic geology of the French Gulch quadrangle: Cali- 

fornio Div. Mines and Geology Spec. Rept. (In press) 

Albers, J. P., and Robertson, J. F., 1961, Geology and ore deposits 
of east Shasta copper-zinc district, Shasta County, California; U.S. 
Geol. Survey Prof. Paper 338, 107 p. 

Allen, J. E., 1941, Geologic investigation of the chromite deposits of 
California: California Jour. Mines and Geology, v. 37, no. 1, p. 
101-167. 

Averill, C. V., 1931, Preliminary report on economic geology of the 
Shasta quadrangle: California Div. Mines, 27th Rept. State Min- 
eralogist, no. 1, p. 2—65. 

1933, Gold deposits of the Redding ond Weoverville quadrangles 

[California]: Colifornio Jour. Mines and Geology, v. 29, nos. 1, 2, 
p. 2-73. 

1935, Mines and mineral resources of Siskiyou County [California]: 

California Jour. Mines and Geology, v. 31, no. 3, p. 255-338. 

1941, Mineral resources of Trinity County; Colifornio Jour. Mines 

and Geology, v. 37, no. 1, p. 8-90. 



62 



Gkology ok Northern Camforma 



Bull. 190 



Brown, G. C, 1916, The counties of Shasta, Siskiyou, Trinity: Colifornio 
Mining Bur., 14th Rept. Stale Mineralogist (1913-1914), pt. 6, 
p. 745-925. 

Cater, F. W., Jr., and Wells, F. G., 1953, Geology ond mineral 
resources of the Gosquet quadrangle, California-Oregon: U.S. Geol. 
Survey Bull. 995-C, p. 79-133. 

Ferguson, H. G., 1914, Gold lodes of the Weoverville quadrongle, 
Colifornio: U.S. Geol. Survey Bull. 540-A, p. 22-79. 

Hershey, O. H., 1910, Origin of gold "pockets" in northern California: 
Mining ond Sci. Press, v. 101, p. 741-742. 

Holi, P. E., 1964, Nickeliferous laterites in southwestern Oregon ond 
northwestern Colifornio: Econ. Geology, v. 59, no. 3, p. 355-396. 

Hundhousen, R. J., 1947, Blue Ledge copper-iinc mine, Siskiyou County, 
California: U.S. Bur. Mines Rept. Inv. 4124, 16 p. 

Irwin, W. P., 1960, Geologic reconnaissance of the northern Coast 
Ranges ond Klamath Mountains, California, with a summary of the 
mineral resources: Colifornio Div. Mines Bull. 179, 80 p. 

1964, Late Mesoioic orogenies in the ultramofic belts of north- 
western California and southwestern Oregon: U.S. Geol. Survey Prof. 
Paper 501 -C, p. C1-C9. 

Kinkel, A. R., Jr., Hall, W. E., and Albers, J. P., 1956, Geology and 
base-metal deposits of the West Shasta copper-zinc district, Shasta 
County, California: U.S. Geol. Survey Prof. Paper 285, 156 p. 



n-ore deposits, Shasta County, 
129, p. 129-136. 



Lamey, C. A., 1948a, Hirz Mountain iro 
California: California Div. Mines Bull. 

1948b, Shosto and California iron-ore deposits, Shasto' County, 

California: Colifornio Div. Mines Bull. 129, p. 137-164. 

MocDonold, D. F., 1913, Notes on the gold lodes of the Corrville dis- 
trict. Trinity County, California: U.S. Geol. Survey Bull. 530, p. 9-41. 



Minerol con 
p. 49-58. 



odities 



lity Co 



Rice, S. i., 1957, Asbestos, in Wright, L. A., ed 

of California: California Div. Mines Bull. 176 
Swinney, C. M., 1950, The Altoono quicksilver mine 

California: California Jour. Mines and Geology, v. 46, no. 3, 

p. 395-404. 
Trosk, P. D., and others, 1950, Geologic description of the manganese 

deposits of Colifornio: California Div. Mines Bull. 152. 378 p. 
Tucker, W. B., 1923, Silver lodes of the South Fork mining district, 

Shasta County: California Mining Bur., 18th Rept. Stote Mineralogist, 

pt. 7, p. 313-321. 
Wells, F. G., and Coter, F. W., Jr., 1950, Chroi 

County, California: California Div. Mines Bu 

p. 77-127. 
Wells, F. G., Cater, F. W., Jr., and Ryneorson, 

deposits of Del Norte County, Colifornio: 

Bull. 134, pt. 1, chop. 1, p. 1-76. 
Wells, F. G., Smith, C T., Rynearson, G. A., and Livermore, J. S., 1949, 

Chromite deposits near Seiod and McGuffy Creeks, Siskiyou County, 

California: U.S. Geol. Survey Bull. 948-B, p. 19-62. 



nite deposits of Siskiyou 
II. 134, pt. 1, chop. 2, 



G. A., 1946, Chromite 
California Div. Mines 




Photo 2. Castle Crogv Shaslo Counly 



CHAPTER III 

CASCADE RANGE, MODOC PLATEAU 
AND GREAT BASIN PROVINCES 









GREAT 



BASIN 



M J A V E 



\ 






o 



DESERT 



O 



TRANSVERSE RANGES 



4- 



PEN! 

« A . 



50 too ISO Mi las 



^ 

\ 



e i 






Page 

65 Geology of the Cascade Range and Modoc Plateau, by Gordon A. Macdonald 
97 Economic mineral deposits of the Cascade Range, Modoc Plateau, and Great 
Basin region of northeastern California, by Thomas E. Gay, Jr. 

[63] 




Cone Mountain. 



64 



GEOLOGY OF THE CASCADE RANGE AND MODOC PLATEAU * 



By Gordon A. Mai Donald 

U.S. Geological Survey and Hawaii Institute of Geophysics, 

University of Hawaii, Honolulu, Hawaii 



Most of the northeastern corner of California, nortli 
of the Sierra Nevada, is included in the physiographic 
provinces of the Cascade Mountains and the Modoc 
Plateau. The Cascade Range extends northward through 
Oregon and Washington into British Columbia, and 
the Modoc Plateau e.xtends into Oregon and southeast- 
ward into Nevada. Most of the Cascade Range is a 
fairly well-defined province, but in northern Califor- 
nia the separation between it and the .Modoc Plateau 
becomes indefinite. The block-faulting characteristic 
of the Modoc region extends into the Cascade Range, 
and the rocks characteristic of the two provinces are 
intermingled. The division between the Modoc Plateau 
and the Great Basin, which borders it on the east, also 
is vague. Both regions consist of fault-block mountain 
ranges separated by flat-floored basins, and similar 
rocks are present on both sides of the boundary. 

The outstanding characteristics of the Modoc region 
are the dominance of volcanism so recent that the 
/ constructional volcanic landforms are still clearly pre- 
served and the presence of broad interrange areas of 
nearly flat basalt plains. It is the basalt plains that have 
given rise to the designation "plateau"; however, the 
region as a whole is far from being the high, essen- 
tially undiversified plain that the term usually implies. 

At the southern end of the region, the rocks of the 
Cascade Range and the Modoc Plateau overlap jhe 
metamorphic and plutonic rocks of the Sierra Nevada; 
50 miles to the northwest, similar rocks emerge from 
beneath the Cascade volcanics at the edge of the Klam- 
ath Mountains province. The broad depression extend- 
ing northeast across the Sierra Nevada-Klamath oto- 
genic belt, originally recognized by von Richthofen 
(1868), was called the "Lassen Strait," by Diller 
(1895a, 1897), who believed it to have been a sea- 
way that in Cretaceous time connected the marine 
basin of California with that of east-central Oregon. 
Sediments deposited in the southwestern end of the i 
strait are represented by sandstones of the Chico For-i 
mation (Upper Cretaceous) which underlie the vol- ^ 
canic rocks of the Cascade Range along the eastern \ 
edge of the Sacramento Valley. Probably this depres- 
sion persisted — though above sea level and disrupted 
by volcanism and faulting — through much of Tertiary 
time. Although the plutonic and metamorphic rocks 
are nowhere exposed within it except in a small area 
adjacent to Eagle Lake, there can be no serious doubt 

* Publication authorized by the Director, U.S. Geological Survey. 



that they underlie the volcanics throughout the area 
of the depression. 

Throughout most of its extent, from nortliern Cali- 
fornia into Washington, the Cascade Range trends 
slightly east of north. However, at Mount Shasta, 40 
'miles south of the California boundary, the trend 
abruptly changes to southeastward. (It is perhaps 
worth noting that the Sutter Buttes, 150 miles to the 
south, lie approximately on the extension of the main 
Cascade trend.) The change in trend of the Cascade 
Range takes place approximately at the north edge of 
the "Lassen Strait," where it intersects the Klamath- 
Sierra Nevada belt; the trend of the southern part of 
the range is parallel to, and probably controlled by, 
the underlying Sierra Nevada structures. The southern 
portion of the range is almost isolated from the north- 
ern part by a projection of metamorphic rocks of the 
Klamath province. Within this portion of the Cascade 
Range, almost certainly underlain by the older oro- 
genic belt of the Sierra Nevada, the variation in rock 
types and the incidence of varieties more acidic than 
andesite appears to be greater than in the northern 
portion of the range, except for the eastern outliers 
of the Medicine Lake Highland in California and the 
Newberry \^olcano in Oregon. 

Although it is distinctly to the east of the Cascade 
Range as a whole (fig. 1), the Medicine Lake High- 
land is generally regarded as an eastward bulge of the 
Cascade province (Hinds, 1952, p. 129). As Anderson 
(1941, p. 350) has pointed out, however, the Medicine 
Lake volcano, like the similarly outlying Newberr\- 
\'olcano (Williams, 1935), differs somewhat from the 
typical volcanoes of the High Cascades. Situated in 
the plateau region, rather than in the Cascade belt of 
otogenic volcanism, these volcanoes may represent an 
evolution of stray Cascade-type magmas under dif- 
ferent tectonic conditions. 

Following Diller's (1895a, 1906) excellent pioneer 
work in the southeastern part of the region, the 
amount of geological work that has been done in the 
Cascade and Modoc provinces of California is surpris- 
ingly little. The areas are shown on a scale of 1:250,000 
on the Weed, Alturas, Redding, and Westwood sheets 
of the Geologic Map of California (California Div. 
Mines, 1958-1964), but published mapping on a larger 
scale is limited to a few widely separated areas. Within 
the Cascade Range these include, near the south end, 
the Lassen \'olcanic National Park (W^illiams, 1932a) 



:65] 



66 



Geology of Northern California 



Bull. 190 



and the region just to the north (Macdonald, 1963, 
1964), and the Macdocl quadrangle (1:125,000) just , 
south of the Oregon border (Williams, 1949). Be- 
t\\een these, the region in the immediate vicinit\' of 
Mount Shasta has also been described and mapped in 
a reconnaissance fashion t\\'illiams, 1932b, 1934). The 
Medicine Lake Highland has been studied and mapped 
by Anderson (1941), but within the .Modoc region 
proper, the onl\- published mapping on a larger scale 
is on the area immediateh- adjacent to Lassen Volcanic 
National Park (Macdonald, 1964, 1965), in and near 
the Pit River valle\- near Alturas (Ford and others. 
1963), and near Eagle Lake (Gester, 1962). Unpub- 
lished studies have been made of the area south and 
west of Lassen Volcanic National Park by G. H. 
Curtis and T. \. Wilson, of the University of Cali- 
fornia; and reconnaissance studies (unpublished) of 
many other areas have been made by Q. A. Aune, 
C. VV. Chesterman, T. E. Gay, Jr., P. A. Lydon, and 
V. C. McMath of the California Division of Alines and 
Geology. George W. Walker, of the U.S. Geological 
Survey, who studied parts of the northern Modoc 
Plateau while preparing the State Geologic Map of 
Oregon, has generously supplied information for this 
paper, and information for the section on Cretaceous 
rocks was supplied by D. L. Jones, of the U. S. Geo- 
logical Survey. 

A generalized geologic map of the northeastern part 
of California accompanies the article by T. E. Gay, 
Jr., on the economic mineral deposits of the Cascade 
Range, Modoc Plateau, and Great Basin regions of 
northeastern California. 

I wish to thank Q. \. Aune, and especiall\- T. E. 
Gay, Jr., of the California Division of Mines and 
Geology, for their constructive criticism of the manu- 
script of this article and for their aid in collecting and 
preparing the illustrations. 

CASCADE RANGE 

The Cascade Range in Oregon is conveniently di- 
vided into the Western Cascade Range and the High 
Cascade Range (Callaghan, 1933; Peck and others, 
1964). The rocks of the VVestern Cascade Range in- ' 
elude lava flows and beds of pyroclastic debris, and ^ 
in places interbedded nonmarinc and shallow marine 
sediments, gradually accumulated in a slowl\- sinking 
trough to a thickness of more than 10,000 feet. Their 
age ranges from late Eocene to Pliocene (Peck, 1964). 
In composition, they are predominantly pyroxene an- 
desite but range from olivine basalt to rhyolite. Rocks 
of the Western Cascade are underlain by Eocene sedi- >. 
mentar\' rocks of the Umpqua Formation and are un- . 
conformably overlain bv Pliocene to Recent volcanic 
rocks of the High Ca.scade Range. The latter are pre- 
dominantly p\ro,\ene andesite, but range in composi- 
tion from olivine basalt to dacite. Early eruptions in 
the High Cascade were almost wholly basaltic an- 
desite and basalt, producing fluid lava flow s that spread 
to great distances and built a broad, gently sloping 



ridge that consisted largel\ of coalescing small shield 
volcanoes and fis.surc-type flows. Pyroclastic material 
was comparativel\' small in amount. In time, however, 
the predominant lavas became more siliceous, the pro- 
portion of explosive eruption increased, and on the 
earlier ridge of lavas were built the great composite 
volcanoes that forn) the conspicuous peaks <jf the pres- 
ent Cascade Range. Rarel\-, domes of dacite were 
formed. Occasional basaltic eruptions, largely from 
eccentric and independent vents, appear to have taken 
place throughout the period of building of the big 
cones and to have continued afterward. 

X'olcanic rocks in the Western Cascade Range differ 
from those of niost of the High Cascade Range pri- 
marily in greater variety of petrographic tvpes, larger 
proportion of pyroclastic rocks, and a pervasive chlo- 
ritic alteration that gives a characteristic greenish hue 
to most of the rocks. The alteration was probably 
related to the period of folding and uplift of the 
Western Cascade, followed by erosion, that preceded 
the building of the High Cascade, and particularly 
to the small intrusions of gabbroic to quartz monzo- 
nitic composition. 

The northern part of the Cascade Range in Cali- 
fornia is much like that in Oregon. Upper Cretaceous 
and Eocene sedimentary rocks are succeeded by green- 
ish volcanics of the Western Cascade series which were 
faulted and tilted eastward and northeastward at about 
the end of the Aliocene (Williams, 1949, p. 14). Ero- 
sion destroyed the constructional volcanic landforms 
and reduced the region to one of rolling hills before 
renewed volcanism built the High Cascade. South- 
ward the volcanic rocks of the Western Cascade are 
overlapped b\' those of the High Cascade, and south 
of the Shasta region rocks belonging to the Western 
Cascade series have not been recognized, although 
volcanic rocks overlain by Pliocene diatomite in the 
gorge of the Pit River ma\- be equivalent to part of 
them in age. 'In the region northwest of .Mount Lassen 
the upper Pliocene Tuscan Formation rests directl\- 
on Cretaceous and Eocene sedimentary rocks, and the 
I Western Cascade volcanics are absent. 

As in Oregon, the lower part of the High Cascade 
sequence in California consists largel)' of p\roxene 
andesite,! with lesser amounts of basalt and minor 
amounts of hornblende andesite and dacite. .\ltliough 
erosion has dcstro\ed the original topographw these 
lavas appear to have built a broad ridge w ith few, if 
any, big cones. .Most of the lavas are probabl)- of latest 
Pliocene age (Macdonald, 1963). In the region south- 
west of Lassen X'olcanic National Park, how ever, some 
of them are of pre-'Lu,scan age (Wilson, 1961). Con- 
tinuing volcanism became more concentrated at dis- 
tinct centers, and more individualized cones were built, 
some of which are shield volcanoes and some com- 
posite cones. The latter included the largest of the 
volcanic mountains, such as Brokeoff Volcano (Mount 
Tehama), which collapsed to form the caldera in which 



1966 



Macdonam): Cascadf Range and Modoc Platkau 



67 




20 40 60 aO 100 Mills 



Figure 1. Map of a part of northern California, western Oregon, 
and southern Washington, showing the principal peaks of the Cascade 
Range and Sutter Buttes lying farther south along the same trend. 

Lassen Peak was later built, Magee Mountain (Crater 
Peak), Burney Mountain, and Mount Shasta (fig. 1). 
In the Lassen region, volcanism culminated in the 
eruption of several dacite domes, some of them onK- 
a few hundred years old, and at Medicine Lake, flows 
and domes of rhyolite obsidian were erupted. Con- 
temporaneously, basaltic volcanism continued with the 
eruption of such flows and associated cinder cones as 
the Callahan and Burnt Lava flows near Medicine 
Lake, and the Hat Creek and Cinder Cone flows in 
the Lassen region. 

With eruptions at Cinder Cone in 1851 and Lassen 
Peak in 191-1—17, and a possible eruption at Medicine 
Lake in 1910 (Finch, 1928), the Cascade Range of 
California must be regarded as a region of still-active 
volcanism. 

Cretaceous ond Early Tertiary Sedimentary Rocks 

Rocks of Late Cretaceous age are exposed at many 
places along the east side of the Sacramento Valley 
from near Folsom, west of the central Sierra Nevada, 



to the area east of Redding; and from the vicinity of 
Shasta \'alley, northwest of Mount Shasta, to and be- 
yond the northern boundary of the State. In these 
areas the\' rest unconformably on the pre-Cretaceous 
rocks of the Sierra Nevada-Klamath Mountains com- 
plex. They have been referred to as the Chico For- 
mation at Chico and Butte Creeks in Butte County 
and as the Hornbrook Formation in northern Siskiyou / 
County (Popenoe and others, 1960). / 

The Chico Formation consists of massive gray, 
buff-weathering, arkosic sandstone, dark-gray to black 
shales, and beds of conglomerate, particularly near the 
base. In the type locality at Chico Creek, where it is 
4,000 feet thick, it has yielded a varied fauna of am- 
monites, gastropods, and pelecypods ranging in age 
from Coniacian to Campanian. 

East and north of Redding, a similar thickness of 
Upper Cretaceous rocks has been described by Po- 
penoe (1943). The lithologies present are much like 
those at Chico Creek, but although the time of depo- 
sition of the rocks in the two areas overlaps consider- 
ably, the section at Redding spans a slightly older seg- 
ment of the Late Cretaceous. 

In the Hornbrook area near the California-Oregon 
boundary, the Cretaceous rocks consist of about 5,000 
feet of conglomerate, sandstone, and siltstone. The old- 
est unit, which rests unconformabl\- on granitic and 
metamorphic rocks, contains marine fossils (Turonian 
to Coniacian), but part of the overlying conglom- 
eratic sandstone is nonmarine. These rocks are in turn 
overlain by 5,000 feet of marine siltstone, with some 
sandy interbeds. This silty sequence was long regarded 
as a part of the widespread Eocene Umpqua Forma- 
tion, but it has been found to contain Late Cretaceous 
fossils in its upper part (Jones, 1959). About 5 miles 
south of Ager, in exposures near the western edge of 
the Copco quadrangle, the section contains a bed of 
coal, in places as much as 6 feet thick, that was at one 
time mined. Fossils discovered in overl\ing shales con- 
firm the Cretaceous age of the coal beds, formerly 
regarded as Eocene. Thus, no rocks that can be posi- 
tively assigned to the Umpqua Formation of early to 
middle Eocene age (Baldwin, 1964) are known in the 
California part of the Cascade Range or Modoc Pla- 
teau provinces. The Late Cretaceous in this area was 
a period of shallow marine sedimentation with some 
nonmarine deposition, in part on swampy flood plains 
in the northern area. Marine deposition in northeast- 
ern California terminated in the latest Cretaceous, and 
there is no^ depositional record for the Paleocene or 
earliest Eocene. 

Deposition in late Eocene time is recorded by the 
Montgomery Creek Formation (Williams, 1932a; An- 
derson and 'Russell, 1939), which was originally in- 
cluded by Diller (1895a) in the lone Formation. The 
Montgomery Creek Formation is exposed along the 
east side of the Sacramento \'alle\- from near Shingle- 
town, 25 miles east-southeast of Redding, northward 



68 



Gkologv ok Northkrn Cai.ikorma 



Bull. 190 




Figure 2. Index map of northeostei 



for about 50 miles to the upper drainage basin of 
Kosk Creek in the Big Bend quadrangle. It is exten- 
sively exposed along the Pit River near Big Bend, and 
some of the best and most easil\' accessible exposures 
are along Highway 299 (fig. 2) ju.st east of Mont- 
gomery Creek, where sandstones and conglomerates 
in a big highway cut contain fossil leaves. In most 
places the Montgomer\- Creek Formation consists pre- 
dominantly of pale-gray massive sandstone, weather- 
ing to buff, that is locally much channeled and cross- 
bedded and commonl\- contains scattered pebbles and 
pebbly lenses. Thick beds of conglomerate, and less 
commonly of silty shale, are present in places. Locally, 
as along Coal Creek in the VVhitmore quadrangle, the 



formation contains thin beds of poor-grade coal that 
have been mined to a small extent in the past. Frag- 
ments of petrified wood are common in some areas. 
The sandstones are poor in ferromagnesian minerals, 
and in general are weakly cemented. Their weak con- 
solidation results in poor exposures; and where valleys 
have been cut into them, the poor consolidation com- 
monly produces extensive landsliding of overlying 
more resistant rocks such as breccias or andesitic lava 
flows of the upper Pliocene Tuscan Formation. Typi- 
cally, the Montgomery Creek Formation rests uncon- 
formably on Upper Cretaceous sedimentary rocks and 
is overlain unconfomiabl\- by Pliocene volcanic rocks. 



1966 



Macdonald: Cascauf Rangk and Modoc Platfal 



69 




Figure 3. Index map of some areo os figure 2, showing location of quadrangles and principal geographic (eotures mentioned 



Western Cascade Volcanic Series 

The rocks of the Western Cascade volcanic series 
form a nearly continuous belt extending along the 
western foothills~of the Cascade Range for 45 miles 
south of the State boundary, and scattered outcrops 
for another 10 miles. They are exposed along High- 
way 99 just west of Weed, but are better seen along 
the road extending eastward along the Klamath River 
from Hornbrook to Copco Lake. The following de- 
scription is largel\- summarized from the report by 
Williams (1949, p. 20-32). 

Near the State boundary, the exposed thickness of 
the Western Cascade volcanics is not less than 12,000 



feet, and may be as much as 15,000 feet. In the north- 
ern part of the Vreka quadrangle, a few thin beds of 
volcanic conglomerate and sandstone of the Colestin 
Formation (upper Eocene) rest unconformably on the 
Hornbrook Formation at the base of the Western 
Cascade series, but farther south these are absent and 
the low est lavas rest directl\- on the Hornbrook For- 
mation or overlap it to rest on the pre-Cretaceous 
plutonic and metamorphic basement. .\ few lenses of 
tuffaceous sandstone and volcanic conglomerate are 
interbedded with the volcanics at higher stratigraphic 
levels, and coal and carbonaceous shale are present east 
of Little Shasta. The volcanic rocks include both lava 



70 



Geology of Northern California 



Bull. 190 



flows and fragmental deposits, the latter being in part 
direct products of volcanic explosion and in part mud- 
flow deposits. 

The lava flows are mostly pyroxene andesite, gen- 
erally with hypersthene more abundant than augite. 
Some contain a small amount of olivine, commonl\' 
replaced by serpentine or iddingsite, or by a mi.xture of 
magnetite and hematite or goethite. A small amount 
of cristobalite or trid\-mite generall)- is present in the 
groundmass. Most flows are betv.een 10 and 30 feet 
thick, but a few exceed 100 feet. Most are dense to 
sparingly vesicular, and most have a well-developed 
platy jointing that results from shearing in the flow 
as slight movement continues during the last stages 
of consolidation. Hornblende andesites and horn- 
blende-bearing pyroxene andesites are relatively rare, 
as are flows of dacite. The Western Cascade lavas in 
northern California are less altered than many of those 
/in Oregon, possibl\-, Williams suggests, because of the 
alxsence of subvolcanic dioritic stocks and related min- 
eralized belts. Particularly- in the upper part of the 
series, how ever, man\- of the andesites are propylitized, 
the feldspars being partly altered to kaolin and the 
p\roxenes replaced by caicite, chlorite, and limonite. 
In man\- andesites, veins and amygdules of opal and 
chalcedony are abundant, and silicified wood may be 
found in the intercalated tuffs, as at Agate Flat, in the 
north center of the Copco quadrangle, just south of 
the State boundary. 

Pyroclastic rocks include well-stratified andesitic 
tuff-breccias and lapilli tufTs, basaltic agglomerates 
composed of rounded lapilli and bombs, and tuffs of 
andesitic, basaltic, dacitic, and rhyolitic composition. 
Rhyolitic tuffs are found chiefly in the upper part of 
the series. Well-bedded rhyolitic lapilli tuffs of air-laid 
origin reach a thickness of nearly 500 feet near the 
head of Shovel Creek in the northern part of the 
.\Iacdoel (1:62,500) quadrangle; and dense dust-tex- 
tured tuffs reach a similar thickness near the head of 
Little Bogus Creek in the center of the Copco quad- 
rangle. Near Bogus School a bed of rhyolitic tuff, 
traceable for more than 5 miles, varies from an in- 
coherent rock, rich in pumice fragments up to an inch 
long, to a compact crystal- vitric tuff nearly devoid of 
pumice fragments. In places, particularly near the base, 
it is streak\- and welded. The rock is an ignimbrite 
formed by an incandescent ash flow. A quarter of a 
mile north of Bogus Creek, a vertical dike of glassy 
rhyolite 10 feet thick, closely resembling the dense 
crystal-vitric tuff, cuts the bottom of the bed. This 
dike is considered to be the filling of a fissure that 
gave vent to the tuff in the same manner as the erup- 
tion of the "sand flow" of 1912 in the X'allcy of Ten 
Thousand Smokes in .-Maska (Williams, 1949, p. 25). 
Welded dacite tuff near the ea.stern foot of Miller 
Mountain, in the west-central part of The Whaleback 
quadrangle, is considered by Williams to belong to 
the Western Cascade series and to unconformably un- 
derlie basalt of the High Cascade series. 



At Sheep Rock, south of Miller Mountain, beds of 
coarse andesitic tuff-breccia containing angular to sub- 
angular blocks up to 4 feet across in a tuffaceous ma- 
trix reach a thickness of 1,600 feet. Individual layers, 
some of them more than 100 feet thick, show only a 
very crude bedding. The deposits re.semble those of 
the Tuscan Formation in the Cascade Range and the 
Mehrten Formation (Miocene and Pliocene) in the 
Sierra Nevada (Curtis, 1957), and like them, are in- 
terpreted as being the products of volcanic mudflows. 
Similar deposits are found northwest of Little Shasta, 
on the south side of Bogus Mountain, and along the 
Klamath River south of Brush Creek, in the northwest 
portion of the Copco quadrangle. 

Several rhyolite domes are found in the vicinity of 
LifETe Shasta, and volcanic necks and plugs of andesite 
and basalt occur near the lower end of Copco Lake 
and in Shasta \'alley. Two necks at .Agate Flat are 
oval in plan, elongated north-south, and approximately 
2,000 by 1,000 feet across. One of the andesite necks, 
at the hairpin turn of the Klamath River a mile below 
the Copco Dam, is noteworth\- for the presence of 
aegirine in veinlets that also contain zeolites and mag- 
netite and as an alteration product of other pyroxenes 
close to the edge of the veinlets (Williams, 1949, p. 
29). Another of the necks has marginal ring dikes that 
dip outward at angles of 60°-80'^. 

Near the end of the Miocene, the entire Cascade 
belt is believed to have been upheaved, perhaps partly 
by arching, but partly by roughl\- north-south fault- 
ing that produced high east-facing scarps like the one 
2,000 feet high described by Thayer (1936, p. 708) 
near Mount Jefferson in Oregon. Similar fault scarps 
are believed by Williams (1942, p. 29) to have formed 
and been buried by later High Cascade favas near 
Crater Lake, Oregon; others ma>' have formed in the 
region just north of Alount Shasta (Williams, 1949, 
p. 52). Still other faults formed horsts along the east- 
ern side of Shasta \'alle\- and one bordering Shasta 
\'alle\' near Yellow Butte (Dwinnell Reservoir quad- 
rangle) must have had a throw of more than 10,000 
feet (Williams, 1949, p. 53). Whether any correspond- 
ing displacements took place in the portion of the 
Cascade Range south of Mount Shasta is not known. 
The fact that the northwesterly trend of this portion 
of the range coincides with the direction of Sierra 
Nevada-Klamath Mountains structures that are be- 
lieved to underlie it suggests that south of Mount 
Shasta the Cascade Range may have shared the his- 
tor\- of uplift of the Sierra Nevada, rather than that 
of the main, nonhern portion of the Cascade Range. 
Some time after the upheaval of the main Cascade 
, Range, fissures were opened on or near the crest of 
, the ridge, and along them new magma rose to the 
surface to build the High Cascade volcanoes during 
Pliocene to Recent times (Williams, 1949, p. 35). The 
new vents appear to have been located somewhat to 
the east of those that supplied the lava of the Western 
Cascade Range (Peck and others, 1964, p. 50). The 



1966 



Macdonald: Cascadf. Rangf and Modoc Plateau 



71 



building of the Cascade Range south of Mount Shasta 
must have been coeval with that of the High Cascade 
Range farther north. 

Tuscan Formation 

The Tuscan Formation is exposed continuously for 
65 miles along the east side of the Sacramento \''alley, 
from near Oroville to 15 miles north of Red Bluff, 
with smaller isolated areas east of Redding. It has been 
shown by Anderson ( 1933a) to consist largely of brec- 
cias formed by lahars, or volcanic mudflows. The east- 
ern part of the Tuscan consists almost entirely of tuff- 
breccia, in beds ranging from about 40 to 100 feet 
thick, and the entire accumulation averages about 
fjOOO feet in thickness. Along Mill Creek Canyon, 
southwest of Lassen Peak, its thickness is about 1,500 
feet (Q. A. Aune, oral communication, 1965). Toward 
its western edge, interbedded volcanic conglomerates, 
sands, and tuffs appear, and still farther west it inter- 
digitates with the strictly sedimentary Tehama For- 
mation (Anderson and Russell, 1939, p. 2 32 )._Its south- 
ern portion rests on the western slope of the Sierra 
-Nevada and overlaps the Sierran metamorphic and 
■pTutonic comple.x, but its northern portion forms part 
of the western slope of the southern Cascade Range. 
Interbedded in the lower part of the Tuscan For- 
mation in the southern part of the area, east of Red 
Bluff, and with the Tehama Formation on the west 
side of the Sacramento \"alley, is 40 to 100 feet of 
gray, white, or pink dacite tuff containing fragments 
of pumice up to a few inches across in a matrix of 
glass and crystal shards. The massive and unsorted 
character of the deposit and the cleanness of the 
pumice vesicles indicates the ash-flow origin of the 
deposit. Even clearer is the evidence along Bear Creek, 
in the Millville quadrangle, east of Redding, where the 
tuff is in places more than 200 feet thick and much 
of it is thoroughly welded, with the elongate black 
glass "flames" characteristic of ignimbrite. This tuff 
is known as the Nomlaki Tuff Member (Russell and 
V'anderHoof, 1931, p. 12-15). \'ertebrate fossils in the 
Tehama Formation 10 feet above the Nomlaki indicate 
a late Pliocene age for the j Tehama and Tuscan For- 
mations and the intercalated Nomlaki. This age is 
confirmed by a gatassium-argon age of 3.3 m.y. for 
the tuff along Bear Creek (Everndon, et al., 1964). It 
appears probable, however, that the tuff along Bear 
Creek was derived from a different source than that 
farther south. 

Individual blocks in Tuscan breccia generally range 
.from 1 to 6 inches across, but scattered blocks are 
commonly as much as 5 feet thick. Many are vesicular, 
and most were quite certainly derived from lava flows. 
Erosion of the formation results in removal of the 
finer material and concentration of the larger blocks 
on the surface, forming the broad stony plains crossed 
by the highways running northeastward from Chico 
and eastward from Red Bluff and Redding. Cross 
sections of the breccias are well displayed near High- 



way 32, along Deer Creek northeast of Chico, along 
Highw ay 36 east of Red Bluff, and less spectacularly 
along Highwa\ 44 and the Miliville-Whitmore Road 
cast of Redding. 

In the main southern area the blocks in the breccia 
are predominantK^basalt, with lesser amounts of ande- 
site; but in the smaller northern area, the\- are pre- 
dominantly andesitic and dacitic, except locally along 
Bear Creek, where basalt is again abundant (Ander- 
son, 1933a, p. 228). The difference in the prevalent 
t\pe of rock among the blocks suggests different 
sources for the breccias of the southern and northern 
areas, and Lydon (1961) believes that the Tuscan For- 
mation is derived from at least four different sources: 
one near Butt Mountain, 9 miles southwest of Lake 
Almanor, and nearl\- due east of Red Bluff; one near 
Alineral, 10 miles south-southwest of Lassen Peak; one 
east of Whitmore, 30 miles east of Redding; and an- 
other, less certain, a few miles farther north, w est of 
Burnew All of these sources lie within the Cascade 
Range, and the Tuscan Formation, including the Nom- 
laki Tuff Member, almost surely is to be regarded as 
a unit within the High Cascade volcanic series. Along 
the edge of the Sacramento \'alley east of Redding, 
it is the oldest unit, resting directly on the Montgom- 
ery Creek and Chico Formations, but in the Mineral 
area it is underlain bv a thin series of basic lava flows. 

In the area east of Redding, the Tuscan Formation, 
with its interbedded late Pliocene (3.3-m.y.) Nomlaki 
Tuff Member, serves to limit the maximum age of the 
overlying lavas, and these in turn indicate a limiting 
age for the widespread Burne\' (or so-called Warner) 
Basalt in the part of the Modoc Plateau just to the 
east. In other areas, however, the Tuscan Formation 
may range through a considerable age span. Q. A. 
Aune (oral communication, 1965) states that along 
Antelope Creek, in the Red Bluff quadrangle east of 
Red Bluff, the upper layers of the Tuscan Formation 
are nearl\' horizontal, whereas the lower layers are 
deformed nearly as much as the underl\ing Cretaceous 
strata. He suggests that the lower part of the Tuscan 
in that area ma\' be considerabh" older than the late 
Pliocene age generally accepted for the formation. 

High Cascade Volcanic Series 

-The time of beginning of High Cascade volcanism 
is difllicult to date precisely. In the region north of 
Mount Shasta the oldest of the High Cascade rocks 
are vounger than the Miocene rocks of the Western 
CascaHes and older than other rocks that are in turn 
overlain by Pleistocene glacial moraines. They have 
been referred to the Phocene, but there is no assurance 
thaTThe moraines in question are not wholly of late 
Pleistocene age, and hence that the older lavas them- 
selves may not have been erupted in the Pleistocene. 
Near the south end of the Cascade Range, northwest 
of Lassen Peak, andesite lava flows of the High 
Cascade rest on the Tuscan Formation (Macdonald, 
1963), which is of latest Pliocene age (Axelrod, 1957, 



72 



Gkology ok Northern California 



Bull. 190 



p. 27). These aniiesitcs cannot, therefore, be older 
than latest Pliocene. They have, however, been much 
eroded, and the original constructional volcanic land- 
forms on them have been dcstroxed to a considerably 
greater degree than on the oldest High Cascade lavas 
between IVlount Shasta and the Oregon boundary. 
Cpnscqucntl)-, it appears unlikely that the latter are 
older than latest Pliocene, and they are more probabls- 
of Pleistocene age. The basic lava flows that underlie 
the Tuscan formation near Mineral are probably the 
oldest exposed rocks in the High Cascade Range of 
California. Conversely, onl\- relatively minor amounts 
of volcanic rock appear to be later in age than the 
>oungcst glaciation. The building of the High Cas- 
cade took place largely in Pliocene and Pleistocene 
times. 



Williams (1949, p. 35) writes. 



"Throughout the southern port of the High Cascades in Oregon 
ond California, Pliocene and early Pleistocene times were char- 
acterized by the growth of a north-south chain of large, flattish 
shield volcanoes built by quiet effusions of fluid olivine basolt ond 
basaltic ondesite. Great diversity had morked the behavior and 
products of the volcanoes that produced the Western Cascade 
series; on the contrary, the volcanoes now to be described [be- 
tween Mount Shosto and the Oregon border in the Mocdoel and 
The Wholebock quadrangles] were extremely uniform in their 
activity; frogmentol explosions seldom interrupted the quiet outflow 
of lava, and the flows themselves varied only slightly in composi- 
tion despite their wide extent." 

The volcanoes include Miller Mountain, Ball Moun- 
tain, and the Eagle Rock shield. On the eastern edge 
of the area a series of similar broad cones, including 
Mount Hebron, south of Butte Valley, the McGavin 
Peak and Secret Spring A4ountain, north of Butte 
V^alley, are cut by faults of large displacement that 
represent the edge of the block-faulted Alodoc Plateau. 
The only signs of e.xplosive activity' are a few thin 
beds of cinders intercalated with the flows on Secret 
Spring ;\lountain, and the remains of cinder (scoria) 
cones on the summits of Horsethief Butte, Ball Moun- 
tain, and a small shield north of the Copco Dam. 
Slightly younger than the basaltic shields is a series 
; of thick flows of hornblende andesite and dacite(?) 
I erupted from the Haight Mountain volcano, in the 
\Bray quadrangle, just northeast of Mount Shasta, 
probably soon followed by the pyroxene andesites of 
Deer Mountain, Willow Creek Alountain, and the 
early andesite flows of Mount Shasta. These rocks 
contain abundant phenocrysts of hypersthcne, augite, 
and labradorite in a pilotaxitic groundmass, with a 
little tridymitc and cristobalite lining cavities. They 
resemble the principal types of andesite composing 
many of the big cones of the High Ca.scade (Wil- 
liams, 1949, p. 40). Still later, eruptions of andesite 
built the Goosencst volcano, olivine basalt flows built 
the stccp-sidcd cone of The Whalcback volcano, and 
finally floods of olivine basalt issued from fissures to 
pour down the valley of Alder Creek and spread over 
large parts of the floors of Butte and Shasta Valleys. 
Small flows of this group dammed the Klamath River 
to form a lake, at least 35 feet deeper than the present 



Copco Lake, whose shorelines are marked by con- 
spicuous deposits of diatomite. 

The histor\' of Mount Shasta itself will be outlined 
on a later page. 

The sequence of events in the area just north of 
1/a.ssen \'olcanic National Park is in general much the 
same as that deduced by Williams in the region north 
of Mount Shasta, outlined above. The earliest lavas, 
which rest on breccias of the Tuscan Formation, lire 
p\ roxenc andesites associated with small amounts of 
iiornblcndc andesite and dacite. These masses, presum- 
ably of latest Pliocene age, are deepl\' eroded, with 
resultant complete obliteration of constructional forms, 
and the position of former vents is indicated onl\' by 
a few small intrusive plugs and a few cindercone rem- 
nants. 1 he predominant lavas are two-pyroxene an- 
desites, commonl\' with small phenocrysts of feldspar 
and (jften of hypersthene. Scattered small phenocrysts 
of olivine are present in some flows, and at Latour 
Butte blocky augite phenocrysts as much as 1 cm long 
are abundant. These andesites were gently folded on 
east-northeast-trending axes and were slightl\' eroded 
before they were covered locall\' by olivine-bearing 
basalts and basaltic andesites considered to be of very 
early Pleistocene age. 

Both the andesites and the basalts w ere then broken 
by a series of northwest- to north-trending faults. 
Next came a succession of eruptions of basalt, basaltic 
andesite, and andesite that built a series of small shields 
and lava cones. Some of the andesites, such as those 
of Table and Badger Mountains, at the north edge of 
Lassen \'olcanic National Park, are very siliceous de- 
spite their very dark color and decidedly basaltic as- 
pect in the field. The Burnev Basalt, a "plateau" basalt, 
rests against the base of the Badger Mountain shield. 
Next came a series of eruptions of andesite that built 
somewhat larger cones, including Crater Peak (gen- 
eralU' known locally as Magee Mountain), and the 
Brokeoff (Tehama) Volcano that later collapsed to 
form the caldera in which Lassen Peak and its asso- 
ciated domes were built. The construction of the big 
composite cones was followed by the extrusion of 
domes and thick flows of dacite. 

Through later Pleistocene and Recent time, basalt, 
basaltic andesite, andesite, and dacite have been erupted 
more or less simultaneously. Man\' of the basalt flows 
are of very large volume and extent, and in range of 
t\pes are identical to the flows of the Modoc region 
to the northeast. One such flow , near Whitmore, cov- 
ers an area of about 25 square miles, .\nother extends 
ncarl\- 30 miles, from near the northwest corner of 
I,asscn Volcanic National Park to about 2 miles south- 
east of Millville, nearly parallel to Highway 44 for 
most of that distance. It covers an area of more than 
50 square miles; and its volume exceeds 1 cubic mile, 
and may be as great as 2. 

A feature of this region that deserves special men- 
tion is the very widespread occurrence of quartz xeno- 



1966 



Macixjnald: Cascadf, Rangk and Modoc Platf.au 



73 



crysts in the lavas. They are most common in the late 
basalts, such as the well-know n quartz basalt of Cinder 
Cone in the Prospect Peak quadrangle (Finch and An- 
derson, 1930), but the>' are found in both basalts and 
andesites ranging in age from late Pliocene to Recent. 
They can be found in the basalt along High\\a\' 89 in 
the pass just north of the Alanzanita Lake entrance to 
Lassen \'olcanic National Park and are abundant at 
Red Lake Mountain, a mile to the northwest. Not 
uncommonl\' they are several inches across, and some 
of them clearly show the comb structure characteristic 
of many quartz veins. There seems to be little question 
that they are fragments of veins picked up by the 
magma in its rise through the underlying basement of 
crystalline rocks. Some show no signs of reaction with 
the enclosing magma, but others are rounded and 
enclosed in thin reaction rims of pyro.xene. 

The region south and west of Lassen \'olcanic Na- 
tional Park has been studied and described by T. A. 
Wilson (1961). After the deposition of the Tuscan 
breccias a big strato-volcano, named by Wilson Mount 
Maidu, rose around a vent located at Battle Creek 
Meadows, near Mineral, in the Lassen Peak quad- 
rangle. The growth of the cone was contemporaneous 
w ith that of the Brokeoff \^olcano, just to the north- 
east. Early eruptions of basaltic andesite were followed 
by later ones of pyro.xene andesite and dacite. This 
_was followed, some 1 Vi m.y. ago (potassium-argon age 
by G. S. Curtis), by the eruption of two enormous 
flows of rhyolite from fissures on the lower slopes of 
the composite cone. One flow is exposed along Blue 
Ridge and Snoqualmie Gulch, 7 miles northwest of 
Mineral, and the other on the Mill Creek Plateau, 5 
miles southeast of Mineral, but both are accessible only 
by minor country roads. These remarkable flow s cover 
an area of about 78 square miles. Their average thick- 
ness is nearly 500 feet and their maximum thickness 
exceeds 800 feet. The total volume is about 7.6 cubic 
miles! They were followed bv eruption of glowing 
dacite avalanches, probably from the same fissures that 
gave vent to the more westerly of the rh\olite flows. 
These avalanche deposits of pumice tuflf-breccia range 
from 100 to 200 feet thick. Their present area is about 
21 square miles, but large amounts of the easily eroded 
material have been stripped away, and the original 
area was probably two or three times as great. The 
original volume of the avalanche deposits was prob- 
ably at least 1 Vi cubic miles. With the eruption of 
more than 8 cubic miles of rhyolite and dacite magma 
from its lower flanks, it is small wonder that the sum- 
mit of Mount Maidu volcano collapsed to form a 
caldera! Later came a series of basalt eruptions that 
built shield volcanoes with summit cinder cones, or 
cinder cones with associated lava flows. One of the 
latter is Inskip Hill, the edge of which is crossed by 
Highway 36 about 20 miles east of Red BluflF. 

Little information is available on the part of the 
Cascade Range between Mount Shasta and the row 
of quadrangles (Whitmore, Manzanita Lake, and Pros- 



pect Peak) which include the northern part of Lassen 
V^olcanic National Park. The stratigraphic relation- 
ships appear to be much like those described for the 
parts of the range to the north and south except that 
in part the basic lavas rest directly on the pre-Creta- 
ceous rocks of the Klamath Mountains. Along High- 
way 299 west of Burne\', on the Hatchet .Mountain 
grade that ascends the fault scarp at the east side of the 
range, are exposed a series of mudflow breccias which 
appear to be too high in the volcanic sequence to be 
equivalent to the Tu.scan Formation. On the same 
highway, 0.2 mile uphill from the 4,000-foot altitude 
marker, massive glowing-avalanche deposits contain 
numerous fragments of w hite to cream-colored pumice 
up to 6 inches long. Similar deposits, exposed for half 
a mile westward, commonl\' contain man\' fragments 
of andesite and dacite. The same or similar beds, one 
of them containing many dark irregular bombs and 
lapilli of andesitic cinder, are conspicuously' displayed 
in roadcuts and a quarry just west of Hatchet .Moun- 
tain summit, interbedded with flows of andesite. These 
rocks appear to be of about the same age as the folded, 
very late Pliocene volcanic rocks in the Manzanita 
Lake quadrangle. 

The Hatchet .Mountain fault, west of Burney, ap- 
pears to be older than the basaltic shield of Goose 
.Mountain (northeast Montgomery Creek quadrangle), 
which is built against the base of the scarp. The cone 
of Burney .Mountain, one of the major peaks in this 
part of the range, appears to be built almost entirely 
of block-lava flows of basaltic andesite, though it ma\-, 
like .Magee Mountain just to the south, have a pyro- 
clastic core (Macdonald, 1963). Burne\- Mountain 
shows no sign of having been glaciated, and at least 
its carapace is probably of Recent age, though it ap- 
pears to be older than the twin cinder cones and 
associated basalt lava flows at its southeast base. 

Just north of the Pit River, the andesites and basalts 
mapped b\' Powers (1932, pi. 1) along the east edge of 
the Cascade Range as his massive lava group also ap- 
pear to be equivalent, at least in part, to the late 
Pliocene volcanic rocks of the Manzanita Lake and 
Whitmore quadrangles. Their original surface forms 
have been destroyed b\' erosion and the\' have been 
severely glaciated, but they are less deformed than the 
nearby rocks of probable Miocene age of the Cedar- 
ville Series of Russell ( 1928) in the .Modoc Plateau and 
have been regarded b\- Powers (1932, p. 2.i9-260) as 
probably of Pliocene age. 

A series of interbedded basaltic and andesitic lava 
flows, mudflow deposits, volcanic sediments, and a 
little diatomite are exposed along the gorge of the 
Pit River west of Lake Britton (Aune, 1964, p. 187) 
and dip in general l.*i'-30° northeastward. They are 
overlain unconformabl\' by diatomaceous sediments 
deposited in a lake that occupied the site of the pres- 
ent Lake Britton but was considerabh' more extensive. 
According to G. Dallas Hanna, the diatoms in these 
sediments are of Pliocene age, probably not younger 



74 



GKOLCXiV OF NoKllllKN CaI.IKJRMA 



Bull. 190 




Photo 1. Mount Shosto. Photo by G. Do//os Hon 



than middle Pliocene (Aune, 1964, p. 187). On that 
basis, Aune infers a Miocene age for the volcanic rocks 
along the Pit River gorge. The latter rocks resemble 
those of the Cedarvilie Series a few miles to the east, 
in Fort Mountain (southeastern Pondosa quadrangle) 
and its southward continuation, and probably should 
be correlated with them. P'urther work probably will 
demonstrate that the late Pliocene and Pleistocene vol- 
canics of the Cascade Range have here buried one of 
the fault blocks of the Cedarvilie Series characteristic 
of the Modoc province. 

Mount Shasta. — The beautiful double cone of Mount 
Shasta is the largest of the Cascade volcanoes. From a 
base about 17 miles in diameter, it rises to an altitude 
of 14,162 feet, some 10,000 feet above the average 
level of its surroundings. Its volume is about 80 cubic 
miles. The slope of the cone diminishes from about 
35 near the summit to i° near the base. The geolog\- 
of Mount Shasta has been described b\- Diller (1895b) 
and Williams (19321), 1934); the following account is 
taken largely from the papers 1)\- Williams. 

To the south and west, the lavas of Mount Shasta 
rest in part on older (late Pliocene?) andcsitcs of the 
High Cascades and slightly altered volcanics of the 
Western Cascades, and in part on metamorphic and 
plutonic rocks of the Klamath Mountains complex. 
Haystack Butte, in the southeast corner of the Dwin- 



nell Reservoir quadrangle, 10 miles north-northwest 
of the summit of the mountain, is a steptoe of the 
latter rocks projecting through basalt and andesite 
flows of Mount Shasta. To the cast, the Shasta flows 
disappear beneath a cover of later volcanics. 

The main cone of Mount Sha.sta is so \'oung that 
onh" its outermost part is exposed by erosion. The 
deepest canyon, that of Mud Creek, on the southeast 
flank, has cut into it only about 1,500 feet. The visible 
portion of the cone consists, according to W'illiams, 
almost entirely of massive, poorly banded, moderately 
vesicular lava. Individual flows attain a thickness of 
200 feet but average onl\- about 50 feet; apparently 
all originated from the single central vent. Block lava 
and aa flows are rare and largely confined to the 
upper part of the cone. The lavas of the basal part of 
tiic cone are predominantlx' basaltic andesite, whereas 
the later lavas of the upper part arc predominantl\- 
p\roxene andesite, with a lesser amount of dacite. 
Some of the latest flows contain basaltic hornblende, 
and the very summit of the mountain consists of sol- 
fatarizcd dacite. P^roclastic materials are present onl\ 
in small proportion. Fragmcntal beds in the walls of 
Mud Creek Canyon, which are among the oldest ex- 
posed rocks of the cone, appear to be mudflovv de- 
posits, and Williams comments (1934, p. 231) that 
mudflows must have been numerous and extensive 



1966 



Macdonai.d: Cascadk Rangi- and Modoc Platkau 



75 



during the rise of the main cone of Shasta, in the 
Pleistocene Epoch, when much of its surface was 
covered with glaciers. 

Late in the history of the volcano, a fissure opened 
across the cone in a nearly north-south direction, and 
along it eruptions formed a series of domes and cinder 
cones with associated lava flows. Gra\- Butte and the 
AlcKenzie Buttes, on the south side of the mountain, 
are domes belonging to this series, and nearb\' Red 
Butte and Signal Butte (formerly called Bear Butte) 
are cinder cones. Gra\' Butte is hornblende-pyroxene 
andesite, and the McKenzie Buttes are glassy dacite. 
On the north flank of the mountain, in northwestern 
Shasta quadrangle, the two prominent hills just south- 
west of North Gate are dacitic domes on the same 
line of fissuring, and North Gate itself marks the vent 
of a young flow of basalt that overlaps the western 
edge of The Whaleback shield volcano. About 2.5 
miles east-northeast of North Gate, a mile south of 
Militar\' Pass, is the steep blocky front of a slightly 
older flow of andesite that originated on the upper 
slope of the main cone in the vicinity of the present 
Hotlum Glacier. 

At the southwestern base of Mount Shasta, just 
west of the line of vents mentioned above, is Everitt 
Hill, a shield volcano with a small cinder cone at its 
summit. Flows of basaltic andesite from this vent e.x- 
tend southwestward down the canyon of the Sacra- 
mento River for more than 40 miles (Williams, 1934, 
p. 2.^5). The columnar-jointed lava, at places over- 
lying river gravels, is well exposed in cuts along High- 
way 99. At Shasta Springs, in the northeastern corner 
of the Dunsmuir quadrangle, a large volume of water 
issues from the base of this flow, where it is perched 
by underlying stream-laid sediments. 

Also very late in the history of the volcano, and 
possibly at about the same time as the development 
of the north-south fissure, an east-west fissure opened 
on the western flank of the mountain. Eruptions along 
this fissure built a small lava-and-cinder cone a mile 
west of the summit, and shortly afterward short thick 
flows of pyroxene andesite began to erupt from an- 
other vent half a mile farther west, building the lateral 
cone of Shastina, which eventually grew to nearly 
rival the main cone in height. The last eruptions 
of Shastina built two small domes and a small dikelike 
plug of hornblende andesite within the crater. Extend- 
ing from a deep notch in the crater rim do\\n the 
western slope of Shastina is Diller Canyon, a \^-shaped 
gash averaging about a quarter of a mile across and 
as much as 400 feet deep. Williams (1934, p. 236) 
suggests that it may hav-e been formed b\' violent 
downward-directed explosions and glowing avalanches 
resembling those of Mount Pelee in 1902, which fol- 
lowed the rise of the domes in the crater. The explo- 
sions and resulting avalanches ma\' have been guided 
by a preexisting fracture. The sides of the can\()n and 
the surface near its distal end are mantled with angular 



blocks of hornblende andesite like that of the domes, 
almost certainly deposited by avalanches, but at tem- 
peratures too low to produce bread-crusting of the 
blocks or alteration of the hornblende crystals on 
their surfaces (Williams, 1934, p. 236). No doubt the 
avalanches modified the form of the mountain slope, 
but whether they alone could have formed the great 
gash remains in doubt. 

The domes in the crater of Shastina are of post- 
glacial age, their surfaces being wholly unmodified b)- 
ice action, although most of the surface of Shasta and 
Shastina was covered by Pleistocene glaciers. On the 
west, ice descended to the level of the valley at the 
base of the mountain, and on the cast ice from the 
Shasta center extended outward over the Modoc Pla- 
teau. Evidence of only one stage of glaciation has 
been recognized, but since the mountain was probably 
in active growth throughout the Pleistocene, deposits 
of earlier glacial stages have probably been buried by 
later lavas. 

At present, the Wintun Glacier, on the east side of 
the mountain, extends down to an altitude of about 
9,125 feet, and on the northwest slope the Whitney 
Glacier reaches about 9,850 feet. The glaciers of 
Mount Shasta have been shrinking rapidly during re- 
cent decades. In 1934 Williams estimated that the\- 
covered an area of slightly more than 3 square miles, 
whereas in 1954 they covered only about 2 square 
miles. In 1895 Diller reported the length of the Kon- 
wakiton Glacier, on the south slope of the mountain, 
to be about 5 miles, but its present length is scarcely 
more than 0.25 mile. Edward Stuhl estimated that dur- 
ing the year 1924 alone the length of the glacier de- 
creased three-eighths of a mile (Williams, 1934, p. 
252). Rapid melting of the snow and ice during dr>' 
years results in torrents of water which issue from the 
snout of the glacier and rush down the canyon of 
Mud Creek. Undermining of the canyon walls, formed 
of old mudflow breccias, sometimes results in land- 
slips that form temporar\- dams, which ma\' then be 
breached to release floods that travel down the can- 
\on to overflow and spread mudflow debris over the 
lower slopes of the mountain. 

Probably even later than the domes in the crater of 
Shastina is a series of block-lava flows of pyroxene 
andesite erupted from progressively lower vents on 
the west flank of the cone, covering an area of nearly 
20 square miles. Like the summit domes, these flows 
are of postglacial age, one of the earliest of them issu- 
ing from vents in the .side of the terminal moraine of 
the \\'hitney Glacier. In the walls of Whitney and 
Bolam Canyons, moraines are exposed beneath the 
lava flows. The surfaces of the flows are almost per- 
fecth' preserved, and the youngest of them probably 
are not more than a few hundreds of years old. 

At the west-southwest base of Aiount Shasta, be- 
tween the towns of Mount Shasta and Weed, High- 
way 99 skirts the base of Black Butte, a dome of horn- 



76 



CiK)l.(XiV OK NORTHIKN CaI.IIORMA 



Bull. 190 



blende andcsitc. The luoiiiuain is about 2,500 feet high 
and 1.5 miles in basal diameter, and owes its almost 
perfectly conical form to the great banks of crumble 
breccia that completely- mantle the solid core of the 
dome e.xcept for a few crags near the top. 

The latest eruptions of Mount Shasta appear to have 
been from the summit \cnt of the main cone; the\ 
produced a deposit of h\ pcrsthene andesite pumice 
and cinder containing blocks, lapilli, and bombs of 
dark glass\' andesite. This deposit mantles the cirque 
heads and forms the Red Hanks on the south side of 
the summit crater (Williams, 1934, p. 231). The final 
explosion, which covered the upper part of the moun- 
tain with a thin layer of brown pumice, may have 
taken place in 1786, when an eruption apparently in 
the general location of Mount Shasta was recorded by 
La Perouse as he cruised along the coast (Finch, 1930). 




Photo 2. Shasta Mountoin. From the Wilkes Exploring Expedition, 
in the niid-19th century. 

At present, the summit crater of Mount Shasta is 
filled by a snowfield about 600 feet across, with a 
small acid hot spring at its margin. When the moun- 
tain was first climbed by E. D. Pearce in 1854, there 
were about a dozen such springs, emitting prominent 
clouds of steam (William.s, 1934, p. 239). The spring 
water contains free sulfuric acid, and ranges in tem- 
perature between about 166°F and 184°F, depending 
on weather and the amount of dilution b\- melt water 
from snow. The rocks \\ithin and around the crater 
are partly opalized and otherwise altered b\' solfataric 
action. 

Lassen Peak rey^iov. — Many of the rocks and struc- 
tures of the region around Las.sen Peak arc directly 
continuous with those of the Manzanita Lake and 
Prospect Peak quadrangles (Macdonald, 1963, 1964), 
mentioned above. Although the oldest rocks of the 
Lassen region are isolated from those to the north by 
intervening younger volcanics, they can be correlated 
with them with considerable certainty. The rocks 
named the Juniper Ande.sitcs by Williams (1932a) arc 



similar petrographicall\ and in degree of deformation 
and erosion to the [ate Pliocene andcsites of the more 
northerly region, and both are clearly overlain by the 
almost-continuousl\'-exposed I'.astern Basalts. The ear- 
lier Willow Lake Basalts of Williams (1932a) are 
probably c(]ui\alcnt to Pliocene volcanic rocks in the 
region northeast of Lassen \'olcanic National Park. 
1 he gcologs' of Lassen N'olcanic National Park has 
been studied in detail b\- Williams, and we cannot do 
better than to (]uote his extended summar\' ( Williams, 
1932a, p. 216-219): 

"The earli< 



ivity seems to be 
Its exposed olong the southern I 
:e of these lavas nothing is o 
wed by the eruption of o th 
!sites, here termed the Juniper 
Juniper Loke for a distonce of 
1 issued from vents that lie con( 



ded in 
of the 



Willow loke 
c, but of the 
'esent known. They were 
series of ploty pyroxene 
s, which extend westward 
( four miles. Possibly these 
d beneath later ejecta in 



the region lying to the east of the Park. At about the same time a 
series of black, porphyritic lavas— the Twin Lakes ondesites- poured 
out from o number of vents on the Central Ploteou, flooding on 
area of at least 30 square miles * * *. Petrogrophicolly, these 
Twin Lakes ondesites ore peculiar by reason of their content of 
quartz xenocrysts, a feature deserving especial mention in view of 
the fact that the lavas lie adjacent to the recently erupted quartz 
basolt of Cinder Cone * * '. 

"At some time following the extrusion of the Twin lakes onde- 
sites, vents opened in the vicinity of White Mountain [northwestern 
corner of the Mount Horkness quadrangle] ond pyroxene ondesite 
flows poured from it, chiefly to the south and east, extending for 
some five miles as far as the head of Warner Valley. To these 
flows the name Flatiron ondesites has been applied. By this time 
the whole eastern portion of the Pork seems to hove been trons- 
formed into a relatively flat lava plain, conspicuously devoid of 
pyroclostic accumulations. 

"The next event was a renewal of activity immediately to the 
east of the Pork, whereby thick flows of pyroxene bosolt— the 
Eastern basalts— were poured out onto the Juniper ondesites. 
Subsequent erosion of these basalts, which may not have extended 
much farther west than at present, produced the rugged hills that 
limit the Pork on the east. Toward the close of this phose of 
activity there were many important pyroclostic eruptions, and 
possibly about the some time— the exact chronology is open to 
doubt-ondesitic ond bosoltic cones were octive along the northern 
boundary of the Pork, in the vicinity of Badger and Table 
Mountains. 

"Meanwhile an enormous volcano had gradually been rising in 



the southwest corne 
about 11,000 feet 



of the 



ultii 



height 



thi! 



but no 
bosolts 
of its e 



lent to the n 

)t improbobl 
being 

d flow! 



Irokeoff Coi 
ime "Tehan 
of telling ' 



tely 
sr of perho 

has been adopted. [This term is 
Volcano" used by other writers.] 
;n the cone commenced activity, 
it was in existence when the Willow Lake 
upted. However that may be, most if not all 
ppeor to be later than the Flatiron lavas. In 
a general way it may be said that the earliest of the BrokeofI 
lavas ore ougite ondesites, above which follow hypersthene onde- 
sites interbedded, toward the top of the cone, with much tuff and 
breccia. The principol vent of this greot volcono loy in the neigh- 
borhood of Supons (Tophet) Springs j now Sulphur Works]. 

"At some period during the later history of the Brokeoff cone, 
fluid lovas were being erupted from four shield volcanoes of 
Hawaiian type, situated one ot each corner of the Central Plateau, 
namely Raker and Prospect peoks. Red Mountain, and Mount Hork- 
ness. By that time the Juniper and Flotiron ondesites hod been 
deeply denuded so that the new lavas poured over an uneven 
surface, many of them spilling down the sides of large valleys. 
Excepting Roker Peak, which is composed of pyroxene ondesite, 
each of these brood, low cones or "shields" consists of pyroxene 
bosolt, and oil four ore surmounted by well preserved cinder cones 
that rise within central, summit craters. 

"The eruptions of Red Mountain had entirely ceased when on 
irregular body of rhyolite was intruded into the cone at its 
northern base; likewise the Roker Peak volcono hod long been 
dormont when a steep.sided, endogenous dome of hornblende-mico 
dactte was protruded through its southern flank * * * 



% 



1966 



Macoonald: Cascadf Rangk and Modoc Platf.au 



77 







Photo 3. Lassen crater on 
June 2, 1914. Phofo by B. F. 
loomis. 









Photo 4. Lassen crater, erup- 
tion of September 29, 1914. 
Photo by B. F. toomis. 




78 



Gk()1.(h;v ok N'oKiiiKKN C^ai.ikornia 



Bull. 190 



Photo 5. Lautn Peak June 
11, 191S. Phofo by B. F. Loomit. 



^jf\ ■*>»*> 




r':.-^ 









»*.^,„.lii*T.^i»£^ 











Photo 6. Volconic bomb from 
Louen Peak eruption, 1915. 
Photo hy B. F. loomit. 



v^.V. 



1966 



Mac;donald: Cascadk Range and Moix)c Pi.atfau 



79 




Photo 7. Lassen "mud flow" May 24, 1915. Photo by B. F. ioom'n 



"Approximately ot this time a new vent opened on the northeost 
slope of the Brokeoff cone, probably close to, if not immediately 
beneath the [present] edifice of Lassen Peak. As for as can be 
judged from the meager evidence this event was unheralded by 
strong pyroclastic explosions. From this new crater streams of fluid 
docite flowed radially, but chiefly toward the north, piling up lovo 
to a thickness of 1,500 feet. These are the black, glassy, beauti- 
fully columnar lavas that now encircle Lassen Peak, here referred 
to as the pre-Lassen dacites. If they ore studied from the base 
upward, it will be found that their content of basic inclusions 
increases more or less regularly until in the topmost dacites of 
Loomis Peak [2 miles west of Lassen Peak] the inclusions may 
constitute as much as half the total volume. Mention is here made 
of this phenomenon because the docite of Lassen Peak itself Is 
likewise heavily charged with similar basic Inclusions. Without 
doubt the large, almost structureless moss of Lassen represents a 
crater filling or plug-dome of Peieon type. The fluid, gos-rlch 
magma has escaped from the crater to form the pre-Lassen flows; 
subsequently the gas-poor dacite, carrying with It abundant frag- 
ments from the hornblendic, basic crust of the magma reservoir, 
welled up sluggishly to build Lassen Peak. As the lava rose, partly 
solid and partly viscous, the margins of the dome were abraded 
and polished against the walls of the vent and the surface of the 
growing pile crumbled continually so as to construct enormous 
banks of talus. 

"Smaller domes of viscous dacite rose to the south of Lassen 
Peak— at Bumpass Mountain, Mount Helen, Eagle Peak, and Vul- 
can's Castle— and some were connected with short, stumpy flows. 
Perhaps at this time also the dacite domes of Morgan and Boy 
Scout Hills were protruded through the southern base of the Broke- 
off Volcano, and the dome of White Mountain was upheoved 
through the vents from which the Flotiron ondesites had long 
before been erupted. Perhaps the domes that border Lost Creek 



also originated at this time. All these domes must hove risen with 
great rapidity compared with the rote of growth of the earlier 
strato-volcanoes. 

"Whether or not the emission of so much dacite was the imme- 
diate cause cannot be determined, but for some reason this phase 
of activity was succeeded by the collapse of the summit of the 
BrokeofT cone along a series of more or less vertical faults, thereby 
producing a vast caldera, approximately 2V^ square miles in extent. 
In its mode of origin this caldera therefore simulates that of Crater 
Lake, Oregon. Many of the principal hot springs of the Lassen 
region are to be found within this faulted caldera of the BrokeofF 

"Lassen Peok had probably risen to its present height when o 
parasitic vent. Crescent Crater, erupted flows of dacite from its 
northeast flank. Then, about 200 years ago, a line of dacite cones 
developed at the northwest base of Lassen, from which showers of 
tuff and pumice were exploded. Two more or less cylindrical bodies 
of viscous dacite, each about a mile In diameter, were subse- 
quently protruded through these cones and now form the Chaos 
Crags. Hardly hod the later, northern dome of dacite been em- 
placed, having risen some 1,800 feet, than steam explosions issued 
from its northern base, causing that whole side of the moss to 
collapse and precipitating a great avalanche of angular blocks 
which lie strewn over an area of 2^/^ square miles, o wilderness 
of debris known as the Chaos Jumbles * * * 

"The complicated history of Cinder Cone, in the northeast part 
of the Park, commenced with violent pyroclastic explosions, pro- 
ducing not merely the cone Itself but mantling on area of more 
than 30 square miles with a sheet of fine ejecta. Possibly this 
occurred about 500 A.D. Subsequently blocky flows of quartz 
bosolt were erupted and after these hod been partly concealed 
by the products of further explosions, there were at least two 



80 



Gkolcx;'* ok Noriukkn California 



Bull. 190 




Photo 8. Losten Peck erup- 
tion, 1915. Photo courtesy of 
Oakland Tribune. 



Photo 9. Cinder Cone, Lassen 
Volconic Notional Pork. This 
area was in eruption in the 
1850s. Phofo by Mory Hill. 




1966 



Macdonald: Cascadf. Rangi. and Modoc Plateau 



81 



Photo 10. Chaos Crags, Chaos 
Jumbles. Pho»o by Robert Stin- 
netf, courtesy of Oakland Trib- 





Photo 1 1 . Manzanita Lake and 
Lassen Peak. Pho(o by Mary Hill. 



82 



Gkolocy of North frn Cam forma 



Bull. 190 




Photo 12 



more eruptions of block/ lovo, the latest of which is reliably doled 
OS occurring in 1851. 

"Steam was seen to be rising from the domes of the Chaos 
Crags as late as 1857, but no further important eruptions took 
ploce in this region until Moy, 1914, when Lassen itself burst into 
activity. For a year explosions recurred ot irregulor intervals. In 
May, 1915, o moss of lava rose into the summit crater, spilling 
over the rim on the northwest and northeast sides and causing 
extensive mud flows by the melting of the snows. On May 22, a 
horizontal blost issued from the northeast side of the crater, 
resulting in further damage along the headwaters of Hot and Lost 
creeks. Thereafter activity declined, finally ending in the summer 
of 1917. Since that dote the volcano hos loin dormant." 

Heath (1960) has shown that the Chaos Jumbles 
were produced by several, probably three, separate 
avalanches. His date of approximately 1700 A.D. for 
the formation of the last portion of the Jumbles, based 
on tree-ring counts and an estimate of the time re- 
quired for establishment of vegetation on the deposit, 
is a good confirmation of Williams' earlier estimate of 
appro.ximately 200 years for the age of the deposit. 



Another e\'ent late in the history of the volcano was 
a glowing avalanche that swept down the valley of 
.Manzanita Creek, northwest of Lassen Peak, depositing 
an unsorted mass of pale-gra>- to white dacite blocks 
and weakly breadcrusted pumice bombs in a matrix 
of dacite ash (Macdonald, 1963). The deposit can be 
seen at the Sunset Campground, west of Manzanita 
Lake, and a small remnant crosses the highway just 
outside the Manzanita Lake entrance to the National 
Park, w here it rests on the Chaos Jumbles. Charcoal 
fragments from the deposit close to the campground 
> ieid a C'' age of less than 200 years (Rubin and Alex- 
ander, 1960, p. 156). The avalanche appears to have 
come from Lassen Peak but ma\' have occurred at 
about the time of the last eruption of the Chaos Crags. 

Brief mention should also be made of the pumice 
ejected during the 1915 eruption of Lassen Peak. The 
pumice is conspicuously banded, \\ ith light streaks of 



1966 



Macdonald: Cascadf. Rangk AM) Modoc Pi.atkau 



83 



dacite and dark ones of andesite. The bands appear to 
represent two distinct magmas, imperfectly mixed at 
the time of eruption (Macdonald and Katsura, 1965). 
Many blocks of this banded pumice can be found in 
the vicinity of the Devastated Area parking lot, near 
the eastern base of Lassen Peak. 

Several groups of hot springs and fumaroles exist in 
and near Lassen Volcanic National Park. Supan's 
Springs, at the Sulphur Works, on Highway 89 near 
the south entrance of the park, issue from andesite 
flows and breccias of the BrokeofF Volcano within the 
caldera, as also do others along Mill Creek and its 
tributaries. Sulphur Creek and Little Hot Springs 
Valley. The springs and fumaroles of Bumpass Hell 
occupy a basin between the dacite dome of Bumpass 
Mountain and the andesites of Brokeoff Mountain. 
Most of the springs contain small amounts (19 to 436 
mg/1) of sulfuric acid, derived from the oxidation of 
H2S in rising magmatic gases, either directly, or by 
oxidation of native sulfur that is in turn derived from 
H2S (Day and Allen, 1925, p. 113, 138). In each spring 
area the highest temperature of the water generally is 
close to the boiling temperature at the altitude of the 
particular spring or fumarole — 91° to 92°C at Bumpass 
Hell and Supan's Springs — but fumarole temperatures 
as high as 117. 5°C have been observed. Depending 
largely on the abundance of the water supply, the 
springs vary from clear pulsating springs to mud pots, 
the spattering of the latter sometimes building enclos- 
ing cones to form mud volcanoes. There are no true 
geysers. The rocks around the springs are altered, ulti- 
mately largely to opal and kaolin, accompanied by 
minor amounts of alunite (Anderson, 1935). The 
structures and textures of the original rocks are often 
almost perfectly preserved in the opalized residuals. 
Where acidity is comparatively high, nearly pure opal 
is formed, but where it is lower, kaolin is the principal 
product. In addition to opal, kaolin, and alunite, the 
sediments in the springs and along their drainage chan- 
nels contain sulfur, pyrite, tridymite, and quartz. The 
two latter minerals may be in part residual from the 
original rocks but appear to have been formed partly 
within the hot springs. 

The area of solfataric alteration within the BrokeofF 
caldera is approximately 5 square miles and is much 
more extensive than the present hot-spring basins 
(Williams, 1932a, p. 259). Solfataric and hot-spring 
activity seems to have been at one time much more 
widespread than it now is. 

Studies by R. W. Bowers and L. C. Pakiser over 
an area of 4,000 square miles in the southern Cascade 
Range and adjoining Modoc Plateau have demon- 
strated an area of negative gravity anomaly that is cen- 
tered in the Lassen region and extends southeastward 
into the Lake Almanor basin (Pakiser, 1964). The 
gravity low, which covers an area of about 2,000 
square miles, has a maximum amplitude of 70 mgals 
and a steep gradient of 8 mgals per mile on the west- 



ern side. Pakiser finds that it can be explained by a 
volume of about 15,000 km^ of light material in the 
outer part of the earth's crust, with a density contrast 
between it and the enclosing rocks of 0.2 grams per 
cm''. Possible explanations of the low-density mass in- 
clude: (1) a batholith of silicic rock beneath the vol- 
canic rocks; (2) a thick accumulation of sedimentary 
rocks beneath the volcanic rocks, deposited in the 
Lassen Strait; (3) a low-density mass caused by ther- 
mal expansion of crustal rocks resulting from vol- 
canic heat; (4) a volcano-tectonic depression filled 
with light volcanic rock. All four may contribute to 
the deficiency of gravity in the area. Certainly, heat- 
ing of adjacent rocks must have occurred during the 
rise of magma through the volcanic conduits, and 
Pakiser (1964, p. 618) considers that this may explain 
the local gravity lows observed in the vicinity of some 
of the volcanoes, such as Lassen and West Prospect 
Peaks. Also, petrographic evidence suggests the fusion 
of crustal material to suppl\' some of the erupted lavas 
(Macdonald and Katsura, 1965, p. 479-480), which 
ma\' have resulted in the formation of a low-densit\ 
batholithic mass beneath the area. Partly because of 
the steep gravity gradient on the western edge of the 
region, the fourth explanation appears the most likels 
for the major part of the anomaly (Pakiser, 1964, p. 
618). Pakiser makes the reasonable suggestion that the 
sunken region was the source of the Nomlaki Tuff 
and that large volumes of low-density ash and other 
volcanic material were deposited in the subsiding 
structure. Similar deficiencies of gravity are found at 
many collapse calderas and volcano-tectonic depres- 
sions in continental regions. 

Medicine Lake Highland. — The Medicine Lake area 
(Medicine Lake and adjacent quadrangles) has been 
studied by C. A. Anderson, and the following brief 
account is abstracted from his report (1941 ). 

The oldest rocks in the region are a series of frag- 
mental deposits of basaltic and andesitic composition, 
correlated by Powers (1932, p. 259) with the Cedar- 
ville Series in the Warner Mountains, 60 miles to the 
east. Similar rocks are widespread in the Modoc region 
north, east, and south of Medicine Lake. They have 
been block faulted, and the lower parts of the fault 
blocks buried by the widespread "plateau" basalts re- 
ferred to by both Powers and Anderson as the Warner 
Basalt. Both the Cedarville Series and the Warner 
Basalt will be discussed in the section on the Modoc 
Plateau; it will suffice here to say that they appear 
to be the basement on which the rocks of the Medi- 
cine Lake Highland accumulated. 

Northwest of the Highland, the Warner Basalt is 
covered by a sheet of massive andesite tuff. Near Dock 
Well, 7 miles northwest of Medicine Lake, the tuff 
is more than 200 feet thick, with no visible stratifica- 
tion. It ranges from gra\- to pink or buff in color, 
and contains pumice fragments commonly up to an 
inch across, in places up to 3 inches across, in a fine 



84 



Geology of North krn Cai.i forma 



Bull. 190 




Photo 13. Bumposs Hell, louen 
Volcanic Notional Pork. Pholo by 
Mary Hill. 



Photo U. Devils Kitchen, Lassen 
Volcanic National Park. Pholo by 
Mary Hill. 




1966 



Macixjnald: Cascadk Rangf and iMoixk; Pi.atfau 



85 



silty matrix. Some of the pumice lapilii are flattened 
and stretched, and the glass is partly devitrified. In 
places the tuflF is slighth- \\elded (Anderson, 1941, p. 
356). There appears to be little question that it is the 
product of a glowing avalanche (pumice and ash 
flow). Its source is unknown, hut probabl)' it is ge- 
netically related to flow s and domes of platy rhyolite 
and rh\olite obsidian that crop out at nine places 
around the base of the Aledicine Lake volcano. These 
obsidians are locally spherulitic, and in the mass be- 
tween Cougar Butte and the road from Lava Beds 
National Monument to Tionesta (Timber Mountain 
quadrangle), lines of spherulites give it a pronounced 
parallel structure. At the same locality, lithophysae 
are lined with cristobalite and small black tablets of 
fayalite (Anderson, 1941, p. 356). At one place on the 
north slope of the Highland, a small mass of stony 
dacite overlies the obsidian. The distribution of the 
rhyolites indicates that the\- are related to a volcanic 
center beneath the present Highland. 

West of Medicine Lake Highland, a group of cones, 
as much as 1,000 feet high, are built of very massive 
basalt containing conspicuous phenocrysts of white 
plagioclase and reddish-brown altered olivine. Some 
of the lava flows must have been quite viscous, since 
the north side of the cone a mile northwest of Pumice 
Stone .Mountain consists of a series of superimposed 
flows, each ending in a steep front, giving the slope a 
terraced aspect (Anderson, 1941, p. 357). The massive 
basalts are probably of about the same age as the 
rhyolites mentioned in the last paragraph. 

The growth of the present Highland began w ith the 
eruption of rather fluid pyroxene andesites, which 
gradually built up a broad shield volcano some 20 
miles across, with a slope of onl\' about 3°. No inter- 
calated p\'roclastic material is found. The flows consist 
of a dark-gra\- vesicular surface portion, 3 to 6 feet 
thick, terminating sharply against an interior medium 
to light-gra\' dense portion characterized by conspicu- 
ous platy jointing. The earliest lavas contain 2 or 3 
percent of small phenocrysts of \'ellow ish olivine, 
whereas the later ones are generall\- olivine free. The 
platy andesites overlie the massive basalts, the ande- 
site tuff, and the rhyolites. They are best exposed on 
the northwest side of the Highland, but most of the 
shield has been buried beneath later volcanics. 

The ultimate height of the shield was probabl\- 
about 2,500 feet, but Anderson (1941, p. 352, 359-362) 
concludes that after the grow th of the shield its sum- 
mit collapsed to form a caldera 6 miles long and 4 
miles wide, w ith its rim some 500 feet below the level 
of the former summit. Lava then rose along the arcuate 
marginal fractures, poured as flows into the caldera, 
and built cones that eventuall>- surmounted the caldera 
rim and allowed some of the later flows to pour down 
the outer slope of the shield. The result was a series 
of eight separate rim volcanoes around the caldera 
which have completeh' hidden the former caldera 



boundaries. The present lake basin is the depression 
left between these rim cones. 

The earliest postcaldera lavas were platy olivine- 
free andesites, resembling the last precaldera lavas. 
Later these gave wa\- to olivine andesites, dacites, and 
rh\olites. The eruptions of plat\- andesite built ridges 
around the north, west, and south of the basin, the 
northern one capped b\- four cinder cones. A small 
mass of perlitic rhyolite is associated w ith the andesite 
in the western ridge. Presumably a similar, hut some- 
what lower, ridge was built on the cast side of the 
basin, since its lavas are exposed northwest of Mount 
Hoffmann, but it is largel\ hidden b\- later volcanics 
of three separate complexes: Red Shale Butte, and 
L\ons Peak, both about 5 miles east of Medicine Lake, 
and Mount Hoffmann, 2 miles east of Medicine Lake. 
\'olcanic activity in the Red Shale Butte complex 
started with eruption of platy olivine andesites resem- 
bling the early lavas of the underlying shield. These 
were followed by the Lake basalt of Powers (1932) 
— a flow of coarsely porphyritic olivine basalt that 
poured into the central basin and now forms the east- 
ern and northeastern margins of .Medicine Lake. The 
Lake basalt contains numerous phenocrysts of white 
plagioclase along with those of yellow-green olivine. 
It was followed by platy andesites, resembling those 
in the ridges north and south of the basin that built 
Red Shale Butte and Lyons Peak. In the latter com- 
plex, some of the lavas are dacitic and contain large 
amounts of brownish glass. In contrast, the Mount 
Hoff^mann complex consists largely of silicic lavas, pre- 
dominantly rhyolites, with basalt flows at the base: 

"The Mount Hoffmann complex is essentially a circular table 
built up by successive outpourings of very viscous perlitic rhyolite, 
each flow ranging from 50 to 150 feet in thickness * * *. The 
closing stages of activity at the summit were marked by the erup- 
tion of a short eastern tongue of perlitic rhyolite, about 100 feel 
in thickness, followed by the protrusion of a dome about 200 feel 
high above the short flow. The two, combined, form a topographic 
dome some 300 feet above the circular table. (Anderson, 1941 
p. 356.) 

"The picture during the late Pleistocene was undoubtedly that 
of a northern ridge of platy andesite passing into the circular table 
of Mount Hoffmann perlitic rhyolite, separated by on ice cop from 
the Red Shale Butte complex of basalt and platy andesites, which 
in turn was separated from the Medicine Mountoin platy andesites 
by a second ice cap. A third covering of ice occupied the broad 
ridge of ploty andesites west of the summit basin ' * *. As the 
ice disappeared. Medicine Lake came into existence, filling the 
summit basin. Continued volcanic activity produced cones and leva 
flows, ond most of the later products show weak or no glaciated 
surfaces and for that reason hove been related to the Recent * * *." 
(Anderson, 1941, p. 367.) 

More than 100 basaltic cinder cones, ranging in age 
from late Pleistocene to Recent, are present in the 400- 
square-mile area of Anderson's map. The\- are scat- 
tered over the entire Highland, on the floor and rim 
of the summit basin as well as on the outer slopes of 
the old shield, and on the surrounding plateau. The 
cones in the summit basin and on the rim "stand alone" 
(Anderson, 1941, p. 36H), but most of the others are 
accompanied by lava flows. Great floods of basaltic 
lava were poured from vents on the north, east, and 



86 



Geology of Northfrn Camfornia 



Bull. 190 



south flanks of the Highland. These were termed the 
.Modoc Basalt 1)\- Powers (1932, p. 272). They include 
the flows of the Lava Beds National Monument. 

"In many pieces the Modoc bosott flows emerged from fissures 
bearing no relationship to cinder cones. One of the most striking 
examples is on the rood north of High Hole Crater [on the south- 
east flank of the Highland], where o fissure supplied port of the 
lava for the Burnt Lava flow. {The rest of the flow came from 
High Hole Crater.) Another good exompte con be seen * * * east 
of Lava Comp (on the northern flonk of the Highland), where 
three fissures discharged bosott to the northern lava field." 
(Anderson, 1941, p. 368.) 

Flows of the Modoc Basalt include nearly aph>ric 
rocks, containing onl\- a few small phenocrysts of 
olivine and an intcrsertal texture that ma\' be seen 
with the hand lens, and porphyritic rocks with con- 
spicuous plagioclase phcnocr\sts in a dark-gra\' apha- 
nitic, microcr\'stalline, hyalo-ophitic to hyalopilitic, 
rarel\- intergranular or intersertal, groundmass. Tlic 
basalts of the latter tvpc grade into andesites. Flows 
of the first t\pe include both pahochoe and aa, with 
pahoehoe predominant. The flows of the second type 
are nearly all aa, grading into block lava, and are 
commonly younger than those of the first t\pe. The 
flows of the Lava Beds National Monument will be 
discussed in the ne.xt section. 

Three very recent basaltic lava flows on the flanks 
of the Medicine Lake Highland are singled out for 
special mention. All three are largel\' aa, but locaih' 
have pahoehoe and block-lava surfaces. Possibly the 
oldest of the three is the flow called the Callahan flow 
by Peacock (1931, p. 269). It covers about 10 square 
miles on the lower northern slope of the Highland. 
The Paint Pot Crater flow (Anderson, 1941, p. 371), 
just southwest of Little Glass Mountain on the south- 
west flank of the Highland, has an area of onl\' about 
1 square mile. Its source. Paint Pot Crater, is a basalt 
cinder cone mantled with a thick la\cr of white pum- 
ice from the eruption of Little Glass Mountain. Pum- 
ice Stone Mountain, just to the north, is an older 
basaltic cinder cone similarly covered by pumice. 
Most picturesque and youngest in appearance is the 
Burnt Lava flow (Peacock, 1931, p. 269-270) on the 
southern flank of the Highland, easily accessible by 
the road that leads southeastw ard from Medicine Lake. 
The lava issued from the vent marked by the cinder 
cone of High Hole Crater and from a fissure just to 
the north. The lava field covers an area of about 14 
square miles, but consists of at least two flows of 
diflFerent age (Finch, 1933): The older is a highly 
oxidized aa exposed near the south end of the field, 
and the younger consists of pahochoe partly over- 
ridden by aa \\ hich has buried a large part of the older 
flow. The lava is basaltic in appearance, but chemi- 
cally it is a basaltic andesite, with a silica content of 
more than 55 percent and a color index of le.ss than 30. 
The same is true of many other flows in the Modoc 
Basalt and other young basaltic flows of the Modoc 
Plateau. 



\'er>' late in the history of the .Medicine Lake 
Highland came a series of silicic eruptions. These in- 
clude: A black, glassy to stony flow of dacite poured 
out on the floor of the summit basin just north of 
Medicine Lake, where it covers about 1 square mile; 
another dacite flow in the gap between Mount Hoff- 
mann and Red Shale Butte; another slightl\' older one 
east of Glass Mountain; a flow of perlitic rhyolite on 
the northeast flank of Mount Hoffmann; a small mass 
of rh\'olite obsidian on the northwest rim of the sum- 
mit basin; and the two striking masses of rhyolite 
obsidian that form Glass Mountain and Little Glass 
.Mountain. The Little Glass Mountain eruption began 
with explosions that showered pumice over the sur- 
rounding country. Fragments of pumice can be found 
as far away as 15 miles to the southwest. Probably a 
cone of pumice was built around the vent, but it was 
cither destro\ed or wholly buried by the ensuing 
flows. Two separate flows were extruded, the second 
completel\- bur>ing the first except at the northeast 
corner. An excellent view of them can be had from 
the summit of Little Mount Hoffmann, which is ac- 
cessible by car. The flow is roughl\- rectangular and 
averages a little more than 1 Yz miles across. Its margins 
are 50 to nearly 200 feet high, and it is probably more 
than 500 feet thick in the middle. Its volume probably 
exceeds 0.1 cubic mile. 

The history of Glass Mountain is more complex 
(.•\nderson, 1933b; Chesterman, 1955). The first event 
was the opening of a fissure trending N. 30° VV., along 
w hich explosions built at least seven cones of pumice, 
the largest at the site of the present Glass .Mountain. 
The surrounding area, particularlv to the northeast, 
w as show ered w irh pumice. Ten miles from the vents 
the pumice la\'er is several inches thick, and near Glass 
.Mountain it is as much as 60 feet thick, with pumice 
blocks up to 2 feet in diameter. At the other cones, 
finely vesicular glass rose in the vents, forming domes, 
most of which breached the cone walls and flowed a 
short distance be>'ond. At Glass Mountain a much 
larger flow issued, pouring mostly eastward to form 
a flow 3'/2 miles long which was split into two tongues 
b\' the slightl\- older mass of dacite mentioned above. 
The eastern tongues are of stony dacite containing 
numerous inclusions of olivine basalt. The dacite 
passes abruptly into rhyolitic obsidian through a tran- 
sition zone in w hich both rock types are present, the 
main part of the flow consisting of rhyolitic obsidian 
devoid of basaltic inclusions (Anderson, 1941, p. 375- 
376). At the end of the eruption, the lava was so 
viscous that it was pushed up into a small dome. Re- 
newed activity resulted in a second, smaller flow that 
partly covered the first. Both obsidian flows have 
pumiceous to scoriaceous surface phases and dense 
glassy interiors. The final stage of activity consisted 
in the rise of a dome of microvesicular rhyolitic glass, 
a quarter of a mile in diameter and 150 feet high, 
w hose summit bristles w ith partly collapsed spines. 



1966 



Macdonald: Cascadk Range and Modoc Platf.au 



87 




Photo 15. little Gloss Moun- 
tain and Mount Shasta from Lit- 
tle Mount Hoffmon. Photo by 
Mary Hill. 



North of Glass Mountain two beds of pumice are 
separated by 6 to 12 inches of soil, showing that the 
eruptions were interrupted by a considerable period 
of quiescence. The upper pumice ranges in thickness 
from a few feet to 30 feet, and contains upright trunks 
of ponderosa pines that were rooted in the soil layer 
on the lower pumice (Chesterman, 1955). Growth 
rings indicate that the largest trees were at least 225 
years old at the time they were killed by the upper 
pumice fall; the interval bet\\'een the two pumice falls 
— making allowance for the time required to establish 
plant growth — is estimated by Chesterman to have 
been around 300 to 350 years. Radiocarbon age deter- 
minations made by W. F. Libby on the tree trunks, 
give a maximum of 1,660 ± 300 years and a minimum 
of 1,107 ± 380 years, with an average of 1,360 ± 240 
years (Chesterman, 1955). The upper pumice thus 
has a probable age of about 1,400 years and the lower 
about 1,700 years. 

Was the Glass Mountain obsidian flow the last erup- 
tive activity in the Medicine Lake region? All of the 
young basalt flows mentioned above have bits of 
pumice and rhyoiitic obsidian scattered over their sur- 
faces, and the Callahan and Paint Pot Crater flows are 
almost unquestionably older than the last silicic erup- 
tions. On the more recent part of the Burnt Lava flow, 
however, the pumice is very small in amount, and has 
probably been blown onto the lava by the wind. The 
flow is close to Glass Mountain, and if it had been 
present at the time of the eruption that produced the 
last thick fall of Glass Mountain pumice, the amount 



of pumice on the flow would be much greater. Ad- 
jacent older lavas and islands within the flow have 
much more pumice on their surfaces, and the pumice 
can hardly have been removed from the exceedingly 
rough surface of the Burnt Lava flow by running 
water. The largest trees growing on the older part 
of the Burnt Lava flow have been estimated to be only 
300 years old, and the surface of the younger part is 
so fresh in appearance that Finch (1933) considered 
that it could easily be less than 300 years old. Char- 
coal samples from a tree stump buried by the flow 
give an age of only 200 ± 200 years (Ives and others, 
1964, p. 49). It appears probable that at least the 
younger part of the Burnt Lava flow is more recent 
than the big eruption of Glass Mountain. The same 
conclusion has been arrived at independently by C. W. 
Chesterman (written communication, 1965). 

Even this may not have been the last eruption! 
Finch (1928) cites a report of a light ash fall that 
coated leaves of plants in the nearby area in 1910 and 
suggests that the ash may have come from a small 
explosive eruption of Glass Alountain. 

Lava Beds National Momivient. — Although the area 
of the Lava Beds National Alonument is geologically 
most closel\- related to the Modoc Plateau, the area is 
located immediately north of the Medicine Lake 
Highland, and it is convenient to discuss the two con- 
tiguously. The rocks of the Monument are the Modoc 
Basalt of Recent age. Most of the surface is covered 
with pahoehoe flows containing numerous lava tubes, 
some of which served as shelters for Captain Jack and 



88 



Gf.oi.ogy ok Nortiikrn C.m.ikorm.'^ 



Bull. IW 



Photo 16. Schonchin Butte, 
Modoc Lavo Beds. Photo b^ 
Mary Hill. 




his band of Modoc Indians during the Modoc War of 
1872-73. Of the .300 lava tubes known within the 
Monument, about 130 have been explored; they range 
from a few feet to about 75 feet in diameter. Some 
have two or three levels, separated b>' nearly horizon- 
tal septa formed by the freezing of the surface of the 
lava stream in the tube during a pause in the lowering 
of the surface of the stream toward the end of the 
eruption. In the lower levels of some caves percolating 
water freezes during the winter to form ice that per- 
sists, only partly melted, through the next summer. 
Lava stalactites are common on the roofs of the caves, 
and occasional stalagmites are found on the floors. 
Quite commonly, an increase in the viscosity of the 



last fluid lava moving through the tube has resulted 
in a change of the lava to aa and the formation of a 
layer of aa clinker on the floor of the pahoehoe tube. 
The roofs of some tunnels have collapsed to form long 
winding trenches, 20 to 50 feet deep and 50 to 100 
feet wide (Stearns, 1928), M'ith occasional short uncol- 
lapsed sections forming natural arches. Tumuli (pres- 
sure domes) are present on the pahoehoe flow surfaces, 
and ropy surface is preserved in places, but most of the 
surfaces are smooth or billowy. 

Less abundant than pahoehoes are flows of aa, such 
as the Devils Homestead flow, that is visible from the 
highway 6 miles north of the Monument Headquar- 
ters. Others include the flow from Schonchin Butte, 





Photo 17. Leva flows from 
Schonchin Butte. Photo by Mary 
Hill. 



1966 



Macdonai.i): Ca.scadk Rangi. AM) Modoc Pi.aikau 



89 



a small flow from Black Crater 2 miles to the north- 
west, and in the southwestern corner of the Alonu- 
ment part of the Callahan flow (known also as the 
Black Lava flow). 

About a dozen cinder cones, 50 to 700 feet high, 
lie within the Monument, and \\ ere formed by mod- 
erately explosive Strombolian-t\pe eruptions at the 
vents of some of the flows. Perhaps the best example 
is Schonchin Butte, just east of the highway 2 miles 
northwest of Monument headquarters. Elsewhere, the 
eruptions were less explosive and built spatter cones, 
commonly in lines along fissure vents. A good example 
of these is the Fleener Chimneys, O.S miles west of the 
highway on a branch road 2 miles northwest of Schon- 
chin Butte — a row of spatter cones built by Hawaiian- 
type eruption at the vents of the Devils Homestead 
lava flow. Some other spatter and driblet cones are 
rootless hornitos, built by escape of gas-charged lava 
through holes in the roofs of underlying lava tubes. 
Mammoth Crater, on the road to Medicine Lake at 
the south border of the Monument, was formed by 
the collapse of the summit of a lava-armored cinder 
cone as a result of lava draining from the underlying 
conduit through a tube in the cone wall. 

Prisoners Rock, at the Petroglyph Section, a few 
miles northeast of the main part of the Monument, 
is a remnant of a cone of palagonite tuff, dissected by 
sub-aerial erosion and cliffed by the waves of ancient 
Tule Lake. Just north of it lies another similar cone. 
These cones resemble Diamond Head and Punchbowl, 
in Honolulu, and Fort Rock and nearby cones in cen- 
tral Oregon, and like them were formed by phreato- 
magmatic explosions where rising basaltic magma en- 
countered water. The cones appear to be older than 
most or all of the lava flows in the main part of the 
Monument. 

Some of the flows in the Monument, particularly 
the Devils Homestead flow, appear to be very recent. 
However, all of them have bits of silicic pumice scat- 
tered over their surfaces and are probably older than 
the last silicic eruptions in the adjoining Medicine 
Lake area. By comparison with flows in other regions, 
Stearns (1928, p. 253) estimated that none of them are 
younger than 5,000 years. 

At the northwest edge of the Monument, Gillem 
Bluff is an excellent example of one of the recent 
fault scarps that are widely distributed over the Mo- 
doc Plateau. It is one of three east-facing scarps that 
form the western side of the Tule Lake basin. 

MODOC PLATEAU 

The Modoc region consists of a series of northwest- 
to north-trending block-faulted ranges, with the in- 
tervening basins filled with broad-spreading "plateau" 
basalt flows, or with small shield volcanoes, steeper 
sided lava or composite cones, cinder cones, and lake 
deposits resulting from disruption of the drainage by 
faulting or volcanism. The oldest rocks are of Mio- 
cene, or possibly of Oligocene age, and the youngest 



are Recent. Although the faulting culminated in late 
Miocene or Pliocene, it has continued into Recent 
time. The Modoc region is best regarded as a part of 
the Great Basin province that has been flooded by 
volcanics, which are perhaps related to the Cascade 
volcanic province. 

Cedarville Series 

Petrographicall\', the Warner Range, which adjoins 
the Modoc Plateau on the east, is a part of the Modoc 
Plateau province. The oldest rocks recognized in the 
Warner Range constitute the (xdarville Series of Rus- 
sell (1928, p. 402-416), divided by him into lower and 
upper units consisting largely of andesitic fragmental 
beds, separated b\- a middle lava member. The lower 
and upper units consist mainly of tuffs, tuff-breccias 
and agglomerates, ignimbrites, and mudflow deposits, 
with a subordinate amount of intercalated andesite lava 
flows. The lower unit contains an abundant middle 
Oligocene flora and a rhinoceros jaw of probable early 
Miocene age (Ga\', 1959, p. 6), and the upper member 
is of late Miocene age (LaMotte, 1936). 

The oldest rocks in the Alodoc region are exposed 
only in the relatively uplifted fault blocks and have 
been tilted, commonl\- between 20° and 30°. Because 
of similarity in lithology and structural relationships. 
Powers (1932, p. 258-259) correlated them with the 
type Cedarville Series of the Warner Range, but 




Lava Beds. Photo by Mary 



90 



Geology of Northern California 



Bull. 190 



pointed out that in {,'cncral there is no indication 
whether the rocks of the Modoc Plateau are equiva- 
lent to the low er or upper unit of the Cedarville, or to 
both. A middle Miocene flora is present in lake sedi- 
ments intercalated with the \-olcanics in the mountains 
between Canb\ and Adin (Gay, 1959, p. 6). 

Little can be added to Powers' (1932, p. 258-259) 
description of the Cedarville Series of the Modoc 
region: 

"The oldest series of volcanic rocks of the area was recognized 
in the field by the abundance of pyroclostic material, tilted ond 
warped structure, and the gentle slopes eroded on its non-resistant 
pyroclostic members. The series shows great range in lithology: 
basaltic flows, intrusives, and pyroclastics; andesitic flows and pyro- 
elastics; and rhyolitic intrusives and pyroclostics * ' *. The basalt 
is typically dark gray to block and has a fine-groined, compact 
texture. Most of the specimens collected hove the ophitic or inter- 
sertol texture common to the typical plateau basalt * * *. They 
ore notable for the presence of chlorophoeite which is not found 
in the younger bosolts of the area * * *. A few of the basalts 
show on intergranulor texture * * *. 

"Andesitic members are most abundant in the series, and of 
these the pyroclostic rocks predominate. The lava specimens col- 
lected are all pyroxene ondesites with both hypersthene and ougite 
OS phenocrysts. Fragments of hornblende andesite ore found in 
detritol material. 

"Rhyolites ore represented chiefly by beds of pumice-tuff. Frag- 
ments of pumice three to four inches in diameter are included in 
a matrix of smaller fragments of the some material. One dike of 
compact, reddish felsite was found which shows a breccioted 
border zone cemented by colorless to white opal." 

Some of the fragmental beds are the tops and bot- 
toms of block-lava flows, and others are mudflow de- 
posits, rather than "pyroclastic" rocks in the sense of 
being direct deposits from explosive activity. Blocky 
flow tops and bottoms are well e.xposed in cuts on 
Highway 299 half a mile east of the Pit No. 1 Power- 
house, interbedded with massive to platy central por- 
tions of the flows. Irregular tongues of the massive lava 
intrude the breccias. Near the top of the same high- 
way grade, a segment of a red cinder cone is inter- 
bedded with the lava flows. Mudflows of the Cedar- 
ville Series are \Kell exposed in cuts along Highway 
299, 8 miles northeast of .'\lturas. 

Rhyolite and rhvolite obsidian in the region near 
Hambone, and at various places within the area of the 
Warner Basalt farther northeast, may belong to the 
Cedarville Series. 

At Hayden Hill, 15 miles south-southeast of Adin, 
gold was formerly mined from an epithermal deposit 
in silicified rhyolite tuff. Gold-bearing veins are also 
present in andesitic volcanic rocks in the Winters 
district, southwest of Alturas, and in rhyolitic rocks 
in the High Grade district, northeast of Alturas 
(Clark, 1957, p. 219). 

Sedimentary rocks are intercalated with volcanic 
rocks of the Cedarville in some areas. Along Highway 
299, where it climbs the western flank of the Big \'al- 
ley Mountains at the cast side of Fall River Valley, 
rhyolitic tuff and tuffaccous sandstone, as well as mud- 
flow breccias, are exposed. Miocene lake beds, includ- 
ing diatomite, crop out farther north in the same 
range, in the mountains to the northeast, at some other 



localities in that area (Gay, 1959, p. 5), and in the 
vicinity of the Madeline Plains 45 miles southeast of 
.■Mturas. 

The Cedarville is probablx- equivalent in age to pre- 
dominantly volcanic formations, such as the Ingalls, 
Dcllckcr, and Bonta Formations of Durrell (1959), in 
the northern Sierra Nevada and adjacent prarts of the 
Great Basin. 

Pliocene Rocks Other Than Warner Basalt 

.About the end of the Miocene Epoch, the Modoc 
Plateau region was shattered by tectonic movements, 
and rocks of the Cedarville Series were broken, tilted, 
and elevated into a series of mountain ranges by fault- 
ing. The drainage system was disrupted, and in the 
basins betu een the ranges, a series of fresh-water lakes 
were formed in which sediments accumulated. Vol- 
canism continued, and lava flows, subacrial and water- 
laid ash beds, niudflow deposits, and the deposits of in- 
candescent ash flows (ignimbrites) were mingled with 
the sediments. In some places the accumulations were 
\\holl\- sedimentar\', elsewhere volcanic layers were 
intercalated with the sedimentary rocks, and in still 
other places the sequence is nearly or entirely vol- 
canic. The lava flows are predominantly mafic, being 
basalts and basaltic andesites; the pyroclastic rocks are 
predominantly rhyolitic. 

Pliocene lake beds are exposed along the valley of 
the Pit River for more than 20 miles west of Alturas, 
for an equal distance southward along the South Fork 
of the Pit River, and for 10 miles northeastward along 
the North Fork. These have been called the Alturas 
Formation by Dorf (1930, p. 6, 23). They include 
diatomite. diatomaceous and tuffaceous silty and sandy 
shale, siltstone, and sandstone. Locally, strongly cur- 
rent-bedded sandstone and conglomerate are probably 
of fluviatilc. rather than lacustrine, origin. The lake 
beds contain a middle Pliocene flora and Pliocene mam- 
malian remains (Gay, 1959, p. 6). Interbedded with 
the sediments southwest of Alturas are la\ers of ignim- 
britc containing man\' lumps of pumice. They can be 
seen along Highway 299, 8 to 10 miles west of Alturas, 
and in the plateau escarpment to the north. South of 
the highway a la>er of welded ignimbritc locally 
forms the resistant caprock of the .\lturas Formation, 
where less resistant overl\'ing lake beds have been 
eroded aw ay. A second, slightly less welded layer lies 
a few feet lower in the section. The rock has been 
quarried for building stone, and the cut stone can be 
seen in the F.Iks Club building (the former railway 
station) in Alturas. Similar ignimbrites are associated 
with lava flows, mudflow deposits, and sediments in 
the mountains farther west, bctw ccn Canby and Adin. 
In a bed well exposed in a highwa\- cut 0.9 mile south 
of AiVrn Pass, some of the lumps of pumice are more 
than a foot long. In the same cut, mudflows of ignim- 
britic debris grade in their upper parts into poorly 
bedded material reworked by water. 



1966 



Macdonald: Cascadk. Range and Modoc Plateau 



91 



Rattlesnake Butte, 10 miles west of Alturas, the type 
locality of the Alturas Formation (Dorf, 1930), marks 
the site of a volcanic vent. The sedimentar>' beds are 
steeply upturned around the central basaltic neck. The 
age of the vent ma\' have been either late Pliocene or 
early Pleistocene. 

According to G. W. Walker (oral communication, 
1965), the uppermost beds that are generally included 
in the Alturas Formation north and west of Alturas 
are nearly horizontal and locally are separated by an 
angular unconformity from the lower part of the for- 
mation. The latter, which contains the beds of ignini- 
brite mentioned above, was faulted and gently folded, 
and was eroded before the deposition of the upper 
beds. In places, however, no unconformity can be 
found, and sedimentation was probably essentially con- 
tinuous throughout the period of accumulation of the 
formation. The upper, horizontal beds contain upper 
Pliocene gastropods and Pliocene or Pleistocene mouse 
teeth (Ga\', 1959, p. 6). Local deformation and enj- 
sion in some areas appears to have been concomitant 
with continued sedimentation in other nearby areas. 

Diatomaceous lake beds are well exposed also around 
Lake Britton, 10 miles north of Burney, and along the 
valley of the Pit River for 5 miles east of the lake. 
They are well displayed where Highway 89 crosses 
the lake, and where Highway 299 crosses Hat Creek. 
Diatoms from these deposits have been studied by G. 
Dallas Hanna, who states that they are of middle and 
late Pliocene age. Similar sediments are found along 
the valley of Willow Creek, southwest of Lower 
Klamath Lake and northwest of the Medicine Lake 
Highland. Still farther northwest, near the village of 
Dorris, sandstones and conglomerates contain non- 
marine gastropods of late Pliocene age (Hanna and 
Gester, 196.3). 

In most areas the lake beds were slightly tilted and 
eroded before they were overlain by the Warner 
Basalt (see ne.xt section). Along Highway 299, about 
7 miles northeast of Alturas, white pumice-lapilli tuffs 
appear to belong to the Alturas Formation, although 
they are tilted at angles greater than 30°. They are 
closely similar to nearly horizontal lapilli tuffs in the 
Alturas Formation a few miles farther west. In the 
area northeast of Alturas they exhibit striking conical 
erosional forms, resembling ha\'stacks or beehives, as 
much as 20 feet in basal diameter and 30 feet high. 

In the southwestern part of the Modoc region, just 
north of Lassen \'olcanic National Park, the uplifted 
fault blocks are composed of andesite lava flows iden- 
tical with, and unquestionably correlative with, the 
post-Tuscan lavas of the adjacent Cascade Range. 
Farther eastward, in the Harvey .Mountain and Little 
V^alle\' quadrangles, similar fault blocks consist of 
basalt and olivine basalt. The very late Pliocene ande- 
sitic volcanism in the Cascade Range gave way east- 
ward to basaltic volcanism. In both areas the bases 
of the fault blocks are submerged in the Burney 
(Warner) Basalt. 



In the southeastern part of the Modoc Plateau re- 
gion, many small shields of basalt and basaltic andesite, 
although considerably eroded, still retain their general 
constructional form. The.se appear to be certainly 
\ ounger than the Pliocene rocks in the fault blocks, 
which have not onl\- been much more disrupted by 
faulting but also have suffered much more erosion. 
The\' are nevertheless older than the widespread 
Warner Basalt and older than Pleistocene lake beds, 
and are regarded as of late Pliocene or Pliocene and 
Pleistocene age. As examples there may be mentioned 
Roop Alountain, 10 miles west-northwest of Susan- 
ville, and several mountains lying between Honey Lake 
and the Madeline Plains. Just north of Lake Britton, 
Soldier Mountain is one of this group, resting against 
the Cedarville Series of the Fort .Mountain fault block. 

Warner Basalt 

The plateau basalt that is widely distributed. be- 
tween the fault-block ranges of the .Modoc region 
is commonly referred to as the Warner Basalt of Rus- 
sell (1928). It was named in the Warner Mountains, 
where R. J. Russell found a sheet of basalt capping 
the Cedarville Series; but Russell (1928, p. 416) be- 
lieved that the same basalt was the most widespread 
unit in the Modoc Lava-Bed quadrangle to the west. 
This was accepted by Powers (1932, p. 266) and 
Anderson (1941, p. 3.53), though both Fuller (1931, 
p. 115) and Anderson recognized that it might not 
be possible to group all of the "plateau" basalt of the 
area into a single stratigraphic unit. .Actually, consid- 
erable variation in both the degree of weathering and 
the thickness of the ash\- soil cover on the basalt at 
different places, as well as other differences in geo- 
logical relationships, indicate that there is considerable 
difference in age of the basalt from one place to an- 
other, and it is preferable to use local formation names 
until the correlation of the basalts throughout the 
region can be more firmly established. The name 
Burney Basalt has been used in this way for the pla- 
teau basalt in the Prospect Peak and Harvey Mountain 
quadrangles (Macdonald, 1964, 1965) and in the Bur- 
ney and Little Valley quadrangles jast to the north, 
and the name Gardens Basalt has been used by Ford 
and others (1963) in the area just northwest of Al- 
turas. For the purpose of this report, however, Rus- 
sell's name Warner Basalt is herein retained as a col- 
lective term for the petrographically and structurally 
similar lavas throughout the region, without any spe- 
cific implication as to contemporaneit>'. 

In the Warner .Mountains the Warner Basalt over- 
lies the tilted upper Cedarville Series conformably, but 
throughout the rest of the region it rests against the 
eroded edges of fault blocks composed of tilted Cedar- 
ville and younger rocks. Since the upper Cedarville 
is of probable late Miocene age, the Warner Basalt in 
the Warner Range cannot be older than late Miocene, 
but the lack of any structural deformation between 
it and the underlying rocks suggests that there may 



92 



Gfoi.(x;y ok Nortiurn California 



Bull. 190 



not be Any grc:ir difference in their ;iges. Both have 
l)een tilted westward with the uplift of the Warner 
Mountains fault block and the basalt appears to he 
overlain by Pliocene volcanic rocks and lake-bed de- 
posits of the Aituras I-"orination. The latter is in turn 
deformed, eroded, and iocalK- overlain by a later scries 
of lake-bed deposits, which in turn is capped by a 
plateau basalt not older than latest Pliocene and prob- 
ably of Pleistocene age (Cjardens Basalt of Ford and 
others, 196.^). In the vicinir\' of Lake Britton also, 
basalt like that of the Warner rests on lower or middle 
Pliocene lake-bed deposits. On Highway 89, 0.8 mile 
north of the bridge across Lake Britton, the lower 10 
to 15 feet of the basalt consists of pillow lava and asso- 
ciated hyaloclastite formed by granulation of the hot 
la\a where it entered water. The lava is conformable 
with the bedding in the undcrKing sediments, and 
poorl\' consolidated sediment was squeezed up into the 
fragmental ba.se of the lava. It is thus unlikeh' that the 
age of this lava is very different from that of the undcr- 
l\"ing sediment. Elsewhere, however, as along High- 
way 299 a mile west of the Hat Creek bridge, Warner 
Basalt can be seen resting unconformably on the same 
series of lake-bed deposits, which had been slightl\' 
tilted and eroded before they were covered by the 
lava flows. Thus even in the small area immediately 
around Lake Britton, there appears to be a consider- 
able range in the age of the l)asalts. Farther south, at 
the north end of the Sierra Ne\ada, Warner Basalt 
lies unconformably on the Penman Formation, which 
is probabl\' of early Pliocene age (Durrell, 19.59, p. 
177-180). .\11 that can be certainl\- said of these lavas 
is that thev are later than the sediments; they could 
conceivablv be as old as middle Pliocene. In the west- 
ern part of the Prospect Peak quadrangle, however, 
the Burne\- Basalt rests against the eroded edges of 
fault blocks of andesite that is in turn younger than 
the Tuscan Formation, of late late Pliocene age, and 
it appears very unlikely that the Burney Basalt is 
older than ver\' earl\' Pleistocene. Thus flows of the 
Warner Basalt probably range from Miocene to Pleis- 
tocene in age. Ga\- and Aune ( 1958, footnote to strati- 
graphic table on explanator\' data sheet) came to the 
same conclusion. 

The largest continuous exposure of the Warner 
Basalt is that of the Gardens Basalt on the high pla- 
teau, commonh' called The Gardens or The Devils 
Garden, that stretches from Aituras westward more 
than 20 miles and northward more than 25 miles, with 
extensions reaching far westward and northward on 
the south and northeast side of Clear Lake Reservoir. 
The total area of the plateau is in the vicinity of 700 
square miles. Other extensive areas of Warner Basalt 
are found in other parts of the region. On Highwa\- 
299 one drives from west of Burney to the rim of 
Hat Creek V'allcv, a distance of 9 miles, confinuousl\ 
over the surface of the Burney Basalt. 



The thickness of the Warner Basalt varies consid- 
erably, even over short distances. In the edge of the 
plateau near Aituras, the Warner Basalt ranges irv 
thickness from 15 to more than 360 feet (Russell, 
1928, p. 418-419). Powers ( 1932, p. 267) believes that 
the average thickness in the area mapped b\- him is 
probably a little more than 100 feet. Individual flow- 
units range from less than 2 feet to more than 50 feet, 
and probably average 4 to 5 feet. Thin units are 
\csicular throughout, but thick ones ma\- be very 
dense in their middle and lower parts. Pipestem vesi- 
cles are conuiion at the base of flow units, but in the 
upper parts the vesicles tend to be spheroidal, with 
forms characteristic of pahochoe. The surface forms 
of the flows also are t\pical of pahoehoe. The surface 
as a w hole is gentl\" undulating, the undulations being 
mostly part of the original surface, but to a lesser 
degree the result of later faulting. In some areas tumuli 
are common. Ropy surfaces can be seen in places. 

In some areas, as on the plateau just east of the 
Hat Creek fault scarp in the Prospect Peak quad- 
rangle, the \ents of the Warner Basalt are marked by 
small- to moderate-sized cinder cones. Elsew here, very 
low shields, sometimes with small amounts of spatter 
still preserved near their summits, were built over the 
vents. Vov the most part, however, the vents were 
probabl)- fissures along which onl\- very small amounts 
of spatter accumulated, as at the vents of the Recent 
Hat Creek flow, described on a later page. Most of 
these vent structures have since been destroyed by 
w eathering and erosion, or were buried b\- outwelling 
lava in a late stage of the eruption, and they can no 
longer be found. 

In hand specimens the Warner Basalt generally is 
medium to light gra\-, with strikingly coarse grain 
and, under the hand lens, with a distinctly' diabasic 
appearance. Small yellowish-green grains of olivine 
arc abundant in most specimens, and occasionally small 
phenocrysts of feldspar are present. Under the micro- 
.scope, the texture is usuallv intcrgranular to sub- 
ophitic, with pale-brown augite ()ccup\ing the inter- 
stices between the feldspar grains. Chemicall\-, the 
rocks are undersaturated, containing normative olivine, 
and are moderately high to ver\- high in alumina. In 
two anal\ses listed b\- Anderson (1941, p. 387) alu- 
mina is 18.5 and 18.2 percent, and total alkalies ap- 
proximatel\' 2.3 percent, with potash ver\' low. A 
sample collected in a railw a>' cut at Tionesta b\- C. W. 
Chestcrman contains 18.5 percent .AL-O:) (Yoder and 
Tillex', 1962, p. 362). However, one collected by Kuno 
(1965, p. 306) from the basalt overlying bright-red 
soil in the cut on Highwa\- 395, just east of the Pit 
River bridge V/2 miles northeast of Aituras, contains 
only 16.8 percent AloO.,. 

The most characteristic feature of the Warner 
Basalt is diktytaxitic structure (Fuller, 1931, p. 116), 
in which many open spaces exist in the network of 
plagioclase plates, as though a late-stage fluid had 



1966 



Macdonald: Cascadk Range and Modoc Plateau 



93 



drained away from between them. Actually, although 
diktytaxitic structure is very common in the Warner 
Basalt, it is not always present; furthermore, it is pres- 
ent in many other basalts in the area, both older and 
younger than the Warner, as in some basalts of the 
Cedarville Series, and among the upper Pleistocene 
and Recent flo\\s, both in the Alodoc Plateau region, 
and in the Cascade Range. It appears to be characteris- 
tic of high-alumina basalts in which feldspar reaches 
saturation and starts to crvstallize at an early stage of 
cooling, rather than of an\' particular stratigraphic or 
structural unit. The uniformity in texture and mineral 
composition of rocks of this magma t\pe, throughout 
the period from Aliocene to Recent, is striking and 
noteworthw 



Pleistocene and Recent Volc< 



Rocks Other Than Wa 



In the region just northeast and east of Lassen Vol- 
canic National Park, there are many small shield vol- 
canoes and lava flows associated with cinder cones, and 
some steeper lava cones that are younger than the 
widespread plateau basalts. The rocks range from oli- 
vine basalt, through basalt, to basaltic andesite and 
andesite. Among the steeper cones are Prospect and 
West Prospect Peaks, at the north edge of Lassen 
National Park, and Sugarloaf, on the west edge of Hat 
Creek \'ailey a few miles farther north. All three have 
cinder cones at their summits. These volcanoes are 
close to the Cascade Range, and perhaps should be in- 
cluded with it. Farther east the cones are all flatter, 
and most of them are typical shields of Icelandic t\pe. 
Among them are Cal Mountain, Cone Mountain, and 
Crater Lake Mountain, just north of Highwa\' 44 in 
the Harve\- Mountain quadrangle. Many of them, like 
Cone Mountain, are crowned by a small cinder cone. 
Crater Lake Mountain is a topical shield, 6 miles across, 
containing at its summit a double collapse crater that 
holds a small lake. South of the highway, rows of 
cinder cones aligned in a north-northwest direction 
mark the vents of basaltic block-lava flows, the steep 
edges of w hich can be seen near the highway. North- 
ward and eastward the abundance of post-Warner 
volcanic rocks decreases, and volcanoes later than the 
Gardens Basalt are nearl>- absent in the northeastern 
quarter of the Modoc Plateau region. 

East of Highway 89, and 6 miles southeast of its 
junction with Highway 299, Cinder Butte is a shield 
built against the base of the Hat Creek fault scarp. 
The position of the vent was probably controlled by 
one of the faults of the Hat Creek system. Another 
shield, 9 miles to the northeast and visible from the 
lookout point on Highway 299 above the Pit River 
Falls, appears to have been the source of the lava flow 
that descended the Pit River canyon at that point and 
now constitutes the ledge of the falls. Like that of 
Cinder Butte, the vent that fed the shield appears to 
have been localized by a fault belonging, in this case, 
to the Butte Creek sNstem. 



It has already been pointed out that the volcanics 
of the Lava Beds National .Monument belong to the 
Modoc Plateau region rather than to the Cascade 
Range or the Medicine Lake Highland. Actually, how- 
ever, it may be more accurate to consider that the 
Modoc and Cascade provinces overlapped during 
Quaternary time. Certainly, in the region just north- 
west of Lassen V^olcanic National Park, the late Pleis- 
tocene and Recent basalt and quartz basalt flows are 
identical in type to those found to the east in the 
Modoc region, and except for the quartz inclusions in 
some flows, are ver\- much like the Warner Basalt. 

Some of the eruptions in the Modoc Plateau region 
are ver\' recent, though with the exception of that of 
Cinder Cone in the northeastern corner of Lassen Vol- 
canic National Park, mentioned earlier, none of them 
are historic. On a line extending northwe.stward from 
Cinder Cone, a flow of basalt block lava from a vent 
between Prospect and West Prospect Peaks is so very 
fresh, and its surface is so well preserved, that it cannot 
be more than a few thousand years old. On the same 
line lie the vents of the Hat Creek flow, believed by 
Anderson (1940) to be less than 2,000 years old. The 
flow occupies the floor of Hat Creek \'alley from 
south of Old Station northward for more than 16 
miles. Highw a\' 89 lies on its surface or close to its 
edge for most of its length. The flow is pahoehoe, with 
a typical undulating surface, in part ropy, and with 
many tumuli. Some of the latter are conspicuously 
displayed along Highwa\' 44 where it crosses the flow 
east of its junction w ith Highway 89. Along much of 
the eastern margin of the flow is a scarp, up to 15 feet 
high. Although it lies along the base of the Hat Creek 
fault scarp, the scarp on the flow is not due to recently 
renewed movement on the fault, but is a slump scarp 
resulting from low ering of the surface of the central 
part of the flow as the lava drained away down the 
valley and shrank due to loss of gas and cooling. The 
Subwa\' Cave is one of several similar caves known in 
the flow (Evans, 1963). It is part of the main feeding 
tube of the flow, formed by the draining away of 
lava out of the tube at the end of the eruption. It can 
be followed for a distance of 2,300 feet, and in places 
is as much as 50 feet in diameter and 16 feet high. The 
flat floor, which represents the congealed surface of 
the lasr fluid lava that flowed through the tube, in 
places shows the clinker\- surface characteristic of aa — 
a common feature in pahoehoe tubes. The Hat Creek 
flow is a fissure eruption. Its vents lie along a line 
trending slightly west of north a mile southwest of 
Old Station. Spatter cones built along the fissure range 
from a few feet to 30 feet high. 

The lava surfaces north and east of Hambone Butte, 
25 miles north of Lake Britton, are ver\' fresh and well 
preserved, and may be nearly as young as the Hat 
Creek flow. The lava appears to have come from a 
vent, or vents, on the south flank of the Medicine 
Lake Highland. 



94 



Gkoi.cxjy of Northkrn Caiiforma 



Bull. 190 



Quaternary Sedimentary Rocks 

Faulting and volcanisni were esscntialls' continuous 
in the Modoc Plateau region from Miocene to Recent 
time. These, together with climatic changes, brought 
about disruptions of drainage and changes of stream 
gradient and regimen, \\ hich in turn resulted in the 
formation of lakes and the deposition of lake and 
stream sediments. The sedimentar\- deposits include 
fanglomerates, stream-laid alluvium and terrace de- 
posits, and tuffaceous sandy, siltv, and diatomaceous 
lake beds, and, in the high mountains, glacial moraines 
and outwash. Lake deposits occupy broad areas in the 
Fall River \'alle\-. Big \'alle\-, the valley of the South 
Fork of the Pit River, the .Madeline Plains, around the 
north end of Lake Almanor, the region around the 
Klamath and Tule Lakes, and smaller areas in other 
basins. Still other basins that appear to be wholly 
floored b\- alluvium may be underlain by lake deposits. 
Deposition of both lake sediments and alluvium is 
continuing in these basins today. 



The dominant structure of the Alodoc Plateau re- 
gion is the very large number of northwest- to north- 
trending faults (fig. 4), man\- of which are so recent 
that the scarps are still well preserved. Most of the 
faults are normal, with little or no suggestion of strike 
slip; but Gay (1959, p. 5) and his coworkers have 
found evidence of major right-lateral mo\'ement on 
the Likel\' fault, which extends southeastward from 
near Canb\- for 50 miles, to the northeastern part of 
the Madeline Plains. (See California I)iv. Mines, 
1958, Alturas sheet. Geologic Map of California.) 
Along this fault, sag ponds and offset drainage lines 
are still visible. On the normal faults, either the east 
or the west side ma\' be downthrown. Some fault 
blocks are tilted, with a visible fault scarp on only one 
side, but others are bounded by fault scarps on both 
sides. The amount of displacement varies from a few- 
feet to more than 1,000 feet. Striking fault scarps are 
so numerous that it is difficult to single out any for 
special mention. Among them are: the scarp more 
than 1,300 feet high on the cast side of Lookout 
Mountain, 5 miles north of Burney; the step-fault 
scarp 1,800 feet high on the west side of Fort Moun- 
tain, 3 miles northeast of the Highway 89 bridge over 
Lake Britton; the scarp ascended by Highway 299 at 
the east edge of Fall River \'alley; the 2,000-foot scarp 
on the west side of Mahogony Alountain, east of High- 
way 97, 7 miles south of Dorris; the series of spectacu- 
lar east-facing scarps west of Tule Lake that are visible 
from Lava Beds National Monument; and the scries of 
scarps near Highway 139 southeast of Tule Lake. A 
low, but beautifull\' preserved, scarp is visible just east 
of Highway 89 about 4/2 miles north of its junction 
with Highway 299. 

The fault scarp along the east side of Hat Creek 
Valley also deserves special comment. At its highest 
point, the scarp, w hich is clearly visible from High- 




figure 4. Topographic map of part of the Prospect Peak quadran- 
gle, showing the Hot Creek fault scarp olong the eostern edge of Hot 
Creek Volley. The ploteou on the right of the scarp is capped with 
Burney Basalt. Sugorioof Peak, on the left, is o late Pleistocene cone 
built largely of ondesite block lava flows. The valley is floored by 
the Hot Creek lovo flow, which only o few thousand years ago poured 
out of inconspicuous vents located 2 miles north of the south boundary 
and 1 mile east of the west boundary of the figure. 

wa\' 89 and is ascended by Highway 44, rises more 
than 1,000 feet above the surface of the Hat Creek 
lava flow. The fault is a comple.x s\stem of subparallel 
c'7/ echelon fractures, the displacement increasing on 
one as it decreases on the adjacent one, with the blocks 
between them commonly constituting inclined ramps 
(fig. 4). The Butte Creek fault system, 3 miles farther 
east, shows a similar pattern (Macdonald, 1964). Fre- 



1966 



Macdonald: Cascade Rancjk and Modoc Plateau 



95 



quent small earthquakes are reported from the Hat 
Creek region, indicating that the Hat Creek fault 
probably is still active. 

Hydrology 

Brief mention should be made of some of the fea- 
tures of the hydrolog\'. Throughout much of the re- 
gion, the high permeability of the surface rocks, typi- 
cal of basaltic terranes, results in a nearly complete 
lack of surface drainage. However, the underlying 
rocks are commonly much less permeable, and the 
rocks of the Cascade Range constitute a barrier to 
the westward movement of the ground water. The 
result is a water table that ranges in altitude from 
about 4,000 to 4,100 feet through much of the Modoc 
Plateau region. Above about 4,000 feet, the Pit River 
and its tributaries and many of the other streams are 
losing water to the ground, but below that altitude 
they are gaining water (R. H. Dale, oral communi- 
cation, 1965). 

Lost Creek disappears completely within a short dis- 
tance of the place where it flows onto the surface of 
that Hat Creek lava flow, and Hat Creek itself loses 
large amounts of water to the same lava flow along 



the upper part of the valley; but the water appears 
again at the Rising River springs (eastern side of the 
Burnev quadrangle), where the lower end of Hat 
Creek X'alley is blocked by less permeable older rocks. 
The upper stretches of Burne\' Creek lose water to 
the permeable Burne\' Basalt and a mile above Burney 
Falls the streambed is usually completely dry; but 200 
million gallons of water issue dail\' from the stream- 
bed within five-eighths of a mile above the falls and 
in the face of the falls in McArthur-Burney Falls State 
Park, \\ here the base of the lava is exposed resting on 
the less permeable rocks beneath. 

The Fall River Springs, 7 miles north of Fall River 
Mills, is one of the largest spring groups in the United 
States, with a flow of about 1,290,000,000 gallons a 
day. This huge discharge is particularK' striking in 
view of the low rainfall in the surrounding region. 
Studies of groundwater gradients by the U.S. Geo- 
logical Surve\' indicate that the water is moving •south- 
ward from the Tule Lake and Clear Lake Reservoir 
areas, 50 miles to the north, beneath and around the 
Medicine Lake Highland (R. H. Dale, oral communi- 
cation, 1965). 



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1935, Alteration of the lavas surrounding the hot springs in Lassen 

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1940, Hot Creek lava flow [California]: Am. Jour. Sci., v. 238, 

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1941, Volcanoes of the Medicine Lake highland, California: Cali- 
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Anderson, C. A., and Russell, R. D., 1939, Tertiary formations of 
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Aune, Q. A., 1964, A trip to Burney Falls: California Div. Mines and 
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Axelrod, D. I., 1957, Lote Tertiary floras and the Sierra Nevada uplift 
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Baldwin, E. M., 1964, Thrust faulting in the Roseburg area, Oregon: 
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California Division of Mines, 1959, Geology of northeastern California: 
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Calloghon, Eugene, 1933, Some features of the volcanic sequence in 
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Chestermon, C. W., 1955, Age of the obsidian flow at Glass Mountain, 
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Clark, W. B., 1957, Gold, in Mineral commodities of California-geo- 
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Curtis, G. H., 1957, Mode of origin of pyroclostic debris in the Mehrten 
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Day, A. L., ond Allen, E. T., 1925, The volcanic activity and hot springs 
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Diller, J. S., 1889, Geology of the Lassen Peak district [California]: 
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1893, Cretaceous and early Tertiary of northern California and 

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1895a, Description of the Lassen Peak sheet, California: U.S. Geol. 

Survey Geol. Atlas, Folio 15, 4 p. 

1895b, Mount Shosto— a typical volcano: Natl. Geog. Soc, Mon. 

1, no. 8, p. 237-268. 

1906, Description of the Redding quadrangle, California: U.S. Geol. 

Survey Geol. Atlas, Folio 138, 14 p. 

Dorf, Eriing, 1933, Pliocene floras of California: Carnegie Inst. Wash- 
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Durrell, Cordell, 1959, Tertiary strotigraphy of the Bloirsden quad- 
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V. 43, no. 3, p. 161-192. 

Evans, J. R., 1963, Geology of some lava tubes, Shasta County: Califor- 
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Evernden, J. F., Savage, D. E., Curtis, G. H., and James, G. T., 1964, 
Potassium-argon dotes ond the Cenozoic mammalian chronology of 
North America: Am. Jour. Sci., v. 262, no. 2, p. 145-198. 

Finch, R. H., 1928, Lassen Report No. 14: The Volcano Letter, no. 161, 
p. 1. 

1930, Activity of a California volcano in 1786: The Volcano Letter, 

no. 308, p. 3. 

1933, Burnt lava flow in northern California: Zeitschr. Vulkonologie, 

V. 15, no. 3, p. 180-183. 

Finch, R. H., and Anderson, C. A., 1930, The quartz basalt eruptions of 
Cinder Cone, Lassen Volcanic Notional Pork, California: California 
Univ. Dept. Geol. Sci. Bull., v. 19, no. 10, p. 245-273. 

Ford, R. S., Soderstrand, J. N., Franson, R. E., Beach, F. H., Feingold, 
S. A., Hail, W. R., Iwamura, T. I., and Swonson, A. A., 1963, North- 
eastern counties ground water investigation: California Dept. Water 
Resources Bull. 98, v. 1, text, 246 p., v. 2, plates. 

Fuller, R. E., 1931, The geomorphology and volcanic sequence of Steens 
Mountain in southeastern Oregon: Washington Univ. Geology Pub., 
V. 3, no. 1, p. 1-130. 

Gay, T. E., Jr., and Aune, Q. A., 1958, Geologic mop of Colifornio, 
Olof P. Jenkins edition, Alturos sheet: California Div. Mines, scale 
1 :250,000. 

Gester, G. C, 1962, The geological history of Eagle Lake, Lassen 
County, California: California Acad. Sci., Occasional Papers 34, 29 p. 

Honno, G. D., and Gester, G. C, 1963, Pliocene lake beds near Dorris. 
California: California Acad. Sci., Occasional Papers 42, 17 p. 

Heath, J. P., 1960, Repeoted avalanches at Choos Jumbles, Lassen Vol- 
canic National Park: Am. Jour. Sci., v. 258, no. 10, p. 744-751. 



96 



CilOI.OCiY OK NORTHFRN CALIFORNIA 



Bull. 190 



Hinds, N. E. A., 1952, Evolution o( the Colifornia londscope: Colifornia 

Oiv. Mines Bull. 158, 240 p. 
Ives, P. C, levin, Betsy, Robinson, R. D., and Rubin, Meyer, 1964, U.S. 

Geologicol Survey rodiocorbon dotes VII: Am. Jour. Sci., Radio- 

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Jones, D. L., 1959, Strotigraphy of Upper Cretaceous rocks in the 

YrekoHornbrook area, northern California |abs.l: Geol Soc. America 

Bull., V. 70, no. 12, pi. 2, p. 1726-1727. 
Kuno, H., 1965, Froctionotion trends of basalt magmas in lovo flows: 

Jour. Petrology (Oxford 1, v. 6, no. 2, p. 302-321. 
LoMotte, R. S., 1936, The upper Cedorville flora of northwestern 

Nevada ond odjocent California: Cornegie Inst. Woshington Pub. 

455, Contrib. Paleontology 5, p. 57-142. 
Lydon, P. A., 1961, Sources of the Tuscan formation in northern Coli- 
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Mocdonold, G. A., 1963, Geology of the Manzanito Lake quodrongie, 

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Geol. Survey Geol. Quod. Mop GQ-345, scole 1:62,500. 
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Mocdonold, G A., and Katsura, Takoshi, 1965, Eruption of Lassen Peak, 

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Russell, R. D., and VanderHoof, V. L., 1931, A vertebrote fauna from 

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Petrology [Oxford], v. 3, no. 3, p. 342-532 



■itschr. Vulkonologic 



15, 



d to Mount Shasta: 
Californio 




^'.:-j>!? 







Photo 19. Basalt pillow lava (Warner bosoll) resting on dioton 
ceous lake sediments along Highway 89 just north of the bridge acr( 
Lake BriHon. The pillows lie in a matrix of hyoloclostite. Diotomite f 
squeezed up into the frogmentol base of the flow. 




Photo 20 
ohoehoe U 



Hornito (rootless spaHer cone) built on t 
a flow in Lovo Beds Notional Monument 



ECONOMIC MINERAL DEPOSITS OF THE CASCADE RANGE, 

MODOC PLATEAU, AND GREAT BASIN REGION OF 

NORTHEASTERN CALIFORNIA 



By Thomas E. Gay, Jr. 
California Division of Mines and Geology. San Francisco 



The minerals industry of this region — about 16,500 
square miles comprising the northeastern corner of 
California — is dominated by three factors: ( 1 ) A nar- 
row range in variety' of rocks, which are predomi- 
nantly Cenozoic basalt and andesite, with local lake- 
laid sedimentary rocks; (2) a low population density 
both in and about the region, creating but minor local 
market demand, and (3) the lack of known commer- 
cial deposits of any mineral commodities except 
pumice, volcanic cinders, and peat suitable for mining 
and shipping to more distant population centers. Al- 
though transportation routes through the region are 
not numerous, rail and highwa)' routes are more than 
adequate to meet the foreseeable demand for hauling 
mineral products. 

The principal mineral commodities of the region, 
all of which are directly related to its volcanic terrane, 
are volcanic cinders, pumice and pumicite, and 
crushed stone — used for railroad ballast, lightweight 
aggregate, and regular aggregate, respectivel\-. \'ol- 
canic products of potential importance are tuffaceous 




Photo 1 Indian mortars and pestles mode fr< 
Modoc Lava Bed Museum. Pholo by Mary H!ll. 



Stone, for dimension stone; perlite, for lightweight ag- 
gregate; and obsidian, sought by rock collectors for 
decorative purposes. Numerous areas of hot springs, 
related to recent volcanic activity in the region, are 
possible sources of geothermal power, but none has 
been developed so far. 

Aletallic commodities are notabl\- lacking in the 
region, although three minor gold districts, minor 
showings of quicksilver, scattered traces of copper, 
and one small uranium deposit are known. 

Lakebed deposits include peat that is being utilized, 
diatomite as \et unused, and salt which has not been 
recovered for many )ears. Stream and flood-plain 
deposits of sand and gravel are used locall>' for aggre- 
gate, but their chemical reactivity owing to excessive 
glass creates a problem. Mainly of historical interest 
are minor showings of low-grade coal; local common 
cla\' deposits formerly used for brick; spring-deposited 
limestone once burned for- local use as mortar; and 
various siliceous materials, such as jasper and petrified 
wood, sought by rock collectors. 

METALLIC MINERAL COMMODITIES 
Copper 

Colorful showings of secondary copper minerals in 
local altered zones in andesitic rocks have encouraged 
minor prospecting at half a dozen localities in the re- 
gion, but no production has resulted. 

Gold 

The Hayden Hill gold-mining district in Lassen 
County and the High Grade and Winters districts in 
iVlodoc County have yielded about $3,500,000 in gold 
and silver, mostly in the early 1900's; however, all 
have long been inactive. 

At Hayden Hill, steeply dipping veins, 1 to 25 ft 
wide, cut Tertiary rhyolitic tuff and breccia. Free 
gold, valued up to $14 per ounce (1915), occurs in 
iron-stained and manganese-rich gouge and ochre 
seams. Workings, as long as 4,500 ft on the level, and 
as deep as 835 ft, followed veins containing oreshoots 
which were reported to be enriched b\- concentration 
b\- descending waters. An estimated total of about 
$2,500,000 in gold, with minor silver, was recovered 
from 1880 to 191 1, and about $50,000 was won during 
the latest period of activity, 1924 to 1934. 



98 



Geology of Northern Cai.iforma 



Bull. 190 




Photo 2. Air photo of Medicine Lake Highland area, showing lava flows. 



Figure 1 (opposite). Geologic mop of portions of Cascade Ronge, Modoc Plateau, ond Great Basin 
provinces in northeastern California. Modified from Weed (1964), Alturos (1958), Redding (1962), West- 
wood (1960), and Chico (1962) sheets of Geologic Map of California. 



1966 



Gay: Cascadf Ranck, Modoc Pi.atkau, Grfat Basin 

122° 121' OREGON 



99 




100 



(;i,()r.(KA oi XoRiiiKKN Cai.iiokma 



Bull. 190 



At High Cirndc, in the iioithciii \V;iincr Range, 
rich but discontinuous oicshoots were found \\ ithin a 
hundred feet of the surface. CJoid occurred mainly in 
narrow stringers in quart/.-tilled, stccpls- dipping silici- 
fied breccia zones and veins in Tertiar\- rh\olite. De- 
spite enthusiastic promotion of tlie camp in 1909-11, 
its productivity was about $75,000 from 1910 to 1919, 
and perhaps 510,000 from 1931 to 1934. Since 1934 it 
has been essentially' inactive. 

The Winters district, near ,\din Summit, comprises 
only the Lost Cabin mine, which in the early 1900's 
yielded about $10,000 from oxidized gold-bearing ore 
occurring in sheared calcitc- and quartz-filled brec- 
ciated zones in 'I"crriar\- andcsite. 

Quicksilver 

At several localities along the east side of Goose 
Lake, Modoc Count>', traces of cinnabar occur with 
chalcedonic silica as vein and scan) fillings in brccci- 
ated, iron-stained, Tertiarx- rhx'olite and interbcdded 
tuff. Despite furnaces (now ruins) built in the 1940's 
and earlier at three localities, and local reports of 
"several flasks" of i]uicksilvcr produced from small 
rich pockets reached b\' shallow workings, no produc- 
tion is recorded. I'.xploration, though sporadic in re- 
cent \ears, was underwa>' in mid- 1965. 

Uranium 

On tiic Nevada line, northeast of Hallelujah Junc- 
tion, Lassen Counts, autunitc and other sccondar\' 
uranium minerals occur in tuffaceous to sandy Ter- 
tiar\- lakeheds that overlap granitic basement. The 
uranium minerals occur ilisscminatcd and in seams, but 
are concentrated in and near woody and lcaf\- organic 
material that is scattered in the lakebeds. In the late 
1950's, open pit mining \ieldcd a number of carloads 
of ore, averaging about 0.5 percent U-0:i, shipped 
from Nevada to Salt Lake City, Utah. Exploration has 
been active in 1964 and 1965, bur production, if any, 
is undetermined. 



NONMETAUIC MINERAL COMMODITIES 
Calcite (optical) 

On the lower east slopes of the Warner Range, 
Modoc Count\-, calcite pods and veins as much as 
2 ft thick yield clear optical-grade calcite, suitable 
for making polarizing prisms and other precision opti- 
cal equipment. 1 he calcite occurs in Miocene ande- 
sitic tuff-breccia of the (xdarvillc Series in two locali- 
ties, just west of Cedarville, and 2 miles north of 
Eaglevillc. .About 1,000 ounces of optical calcitc from 
the more southerI\- location were sold in 1920 and 
1921. This shipment included usable crystals as large 
as 12 inches. .An adtlitional undetermined quantity' was 
reco\ercd from this deposit during World War II for 
use in gunsights. In tiic late I940's about 1,000 pounds 
of chcmicall_\' pure calcitc from the same deposit were 
sold as a standardizing agent for testing acids, but no 
subsequent production is known. 





Photo 3 (left) and 4 (above). Mining volcani( 
for garden slone from the Little Glass Mountain 
Pfioto by Mary Hill. 






1966 



Gav: Cascadk Rangf, iModoc Platfal, Grkat Basin 



101 




Photo 5. Foce of on obsidian 
flow, Siskiyou County. Photo by 
Charles W. Cheiterman. 



Clay 

Common clay, mostly alluvial soil, was quarried in 
the late IROO's, from several localities near the early 
towns of the region; it was burned in field kilns to 
make bricks for local buildings. 

Coal 

Thin seams of low-grade coal, and man\- \\ eathered- 
out fragments, occur in Tertiar\- lakebeds and volcanic 
sedimentar)' rocks in various parts of the region, but 
not in commercial quantity or qualitw 

Decorative Stone 

\'arious decorative limy spring deposits and siliceous 
rocks such as jasper, chalcedony, and petrified wood, 
are hunted b\- mineral collectors ("rockhounds") in 
the region. Obsidian also is sought, but it is discussed 
separately in this article as it has another use. Favorite 
collecting localities are in the eastern desertlike areas, 
especialh- near hot springs, in the \\'arner Range, and 
in parts of the terrain underlain by the Tuscan For- 
mation. 

Diatomite 

Some of the lakebed deposits scattered throughout 
the region, and ranging in age from Early Tertiary to 
Recent, contain potentiaIl\- commercial deposits of 
diatomaceous earth. These deposits are from a few 
feet to several hundred feet thick, and some are ex- 
posed over tens of square miles. \'arying amounts of 
volcanic ash are present in man\' of the localities, but 
portions of most of the deposits are relatively' pure 



diatomite and potentialh usable. Some deposits are 
parti)' covered by thin basalt flows. 

These diatomite deposits have not been completely 
surve\'ed or analyzed for potential usefulness, and no 
diatomite from this region has been sold commer- 
cialh', although freshwater lakebed diatomite has been 
quarried in Oregon and in Nevada. 

The principal diatomite deposits of the region are 
the Pliocene beds around Lake Britton, northeast 
Shasta County, and in Willow Creek \'alley, northeast 
Siski\'ou Count\'. Less extensive exposures occur near 
Alturas, Modoc Count)'; near Da)', south\\est Modoc 
County; near Karlo and Long \"alley, Lassen County; 
and adjacent to Copco and Lower Klamath Lakes, 
Siskiyou Count)'. 

Hot Springs 

A large number of hot springs found throughout 
the region apparentl)' are related to the recency of 
volcanic eruptive activity and the abundance of fault- 
ing. The 28 hot springs shown on figure 2 arc all 
described by Waring (19L^, p. 115-144) as hotter 
than 90°F. In 1963 sources of geothermal power were 
sought b)' explorator)' drilling about 2 miles north of 
Lake Cit)', in Surprise \'alle)', about half a mile west 
of the area of recently active mud volcanos described 
by White (1955), but no development resulted. 

Limestone 

Small vein and spring deposits of limestone, of vari- 
able purit)', were quarried and burned to make lime 



102 



Geology ok Northfrn Cai.iforma 

121* 



Bull. 190 




Dapotit or protptcl 
T 
Hoi iprini 
Au - Qold 
Hi - Quicktllvit 

U - Uronlua 
•c - Opiici I cilcito 

d - D i • t OB i t i 
ob - Obttditn 
pool • Plot 
pi - Po r I i 1 
pu - Puaici. puaiclto 
If - Sand ind |rt«ol 
•c - SI ont. Cf uthod 
Id - Steno. dlMnilan 
*c - Volcinic cinddfi 



Figure 2. Mop thowing the location of hot springs ond deposits of economic mineral commodities 



ortheostern California. 



1966 



Gay: Cascade Range, Modoc Plateau, Great Basin 



103 



mortar for local building in various towns of the 
region, mainly during the 1800's. 

Obsidian 

Quaternary obsidian masses in the Medicine Lake 
Highland and in the Warner Range are sites of avid 
mineral-collector activity. Chatoyant ("rainbow") ob- 
sidian and red-streaked obsidian from the Warner 
Range are especiall\' prized for cutting and polishing. 
Apparently, several thousand dollars worth of obsidian 
from the Warner Range was sold in the 1960's, and 
a large number of claims were staked covering de- 
sirable deposits. An unusual development came in the 
early 1950's, when several large pieces of clear obsidian 
from Glass Mountain, Siskiyou County, were cut and 
polished to make experimental industrial mirrors. 



Recent accumulations of hypnum peat moss in the 
Pleistocene lake basin of Jess Valley, Modoc County, 
are the only source of peat moss in California. The 
usable peat la_\'er is about 300 acres in area and about 
3 1/2 ft thick, lying beneath a foot of overburden. 
The deposit, which has been mined since 1939, yields 
in excess of 10,000 tons of peat moss a year. After the 
overburden is stripped, the peat is piled to dry for 
2 months, then screened, shredded, and bagged in 80- 
pound bales at Likeh' for truck and rail shipment. 
The peat moss is used throughout California and seven 
western states for soil conditioner. 



Four deposits of perlite in the region were pros- 
pected and tested for lightweight aggregate in the late 
I940's, but no production has resulted. These deposits 
are perlitic phases of Tertiary rhyolitic intrusions and 
flows, two at Sugar Hill, Modoc County; one at Cou- 
gar Butte, northeast Siskiyou County; and one at Hot 
Springs Peak, north of Honey Lake, Lassen County. 
A number of other perlite deposits that have not been 
tested occur with rhyolitic rocks in the region; one 
of the largest is in Battle Creek Canyon, Tehama 
County. 

The first perlite to be tested for commercial expan- 
sibility in California was several hundred tons from 
Sugar Hill, shipped to Campbell, Santa Clara County, 
for the test in 1947. The availability of good quality 
perlite in large, uniform deposits much closer to the 
main centers of use, is mainl\' responsible for the lack 
of utilization of these more remote deposits. 

Petroleum and Gas 

Cretaceous and Early Tertiary units that yield gas 
in the Great Central \'alley Province, also contain gas 
where they project eastward beneath the Tuscan For- 
mation in the Cascade Province (Safonov, 1952, p. 
96). Indicated favorable structures east of Cotton- 
wood, northeast of Red Bluff, and east and northeast 
of Corning have been drilled in a few places, but no 
production has resulted. 



Pozzolan 

The rhyolitic Nomlaki Tuff, and other tuffs in the 
Tuscan Formation, have been discussed by Faick 
(1963, p. 714—717) as potential sources of natural 
pozzolan. Other occurrences of vitric tuffs and sili- 
ceous volcanic sediments scattered through the region 
may also be suitable for use as pozzolan should a mar- 
ket develop. 

Pumice and Pumicite 

.About 30,000 tons of pumice and pumicite (about 
one-third of California's annual production) are mined 
each \ear in this region, with almost all coming from 
deposits at Glass Alountain, eastern Siskiyou County. 
The quarrying of pumice and pumicite (particles of 
pumice smaller than 4 mm) began in this region in the 
mid 1940's and through 1965 totaled about 500,000 
tons. The deposits of the Glass Mountain area consist 
of loosel\- consolidated grayish-white rhyolite pumice 
tuff breccia of Recent age. The tuff breccia occurs in 
a blanket that ranges in thickness from 1 to 60 feet, 
and extends over about 10 square miles northeast of 
.Medicine Lake Highland, eastern Siskiyou and west- 
ern Modoc Counties. 

After the overgrowth and thin soil overburden is 
removed, the pumice is quarried in broad pits by 
scraper loaders, and trucked about 10 miles to Tionesta 
for screening and rail shipment, or to pumice block 
plants near Perez, Modoc Count)-. About 75 percent 
of the pumice is made into blocks in the area, for 
shipment throughout northern California and Oregon; 
about 25 percent is shipped in bulk to the San Fran- 
cisco area, where it also is used to make lightweight 
building block. Sized pumice costs about $2.20 per 
short ton at the railhead. 

Several hundred tons of pumice scouring blocks are 
sawed each \ear from a pumiceous obsidian crust atop 
Glass Mountain. 

Salt 

Brine pumped by w indmills from shallow wells and 
ponds in unconsolidated Recent lake sediments east 
of Middle Surprise Lake once yielded a small tonnage 
of crude salt b\' solar evaporation. The salt was used 
locally for stock feed in the early 1900's; the salt 
works has been inactive since 1925, and is almost 
obliterated. 

Sand and Gravel 

Most towns throughout the region have local sources 
of sand and gravel used in small noncommercial quan- 
tities for Portland cement concrete and asphalt con- 
crete aggregate. Owing to its high content of glassy 
volcanic rocks, much of the sand and gravel in the 
region is too reactive for high-specification portland 
cement concrete, although it is commonl\' used for less 
exacting purposes in local road construction. High- 
way-building contracts commonh' specify crushed 
stone, or require sand and gravel hauled from deposits 
outside this region — especialh- for curbs, gutters, and 
bridges. 



104 



Gf.ology of Northkkn California 



Bull. 190 




Photo 6. Volcanic cinder quorry on the southeo n ; 3 

Butte neor Tionesta, Modoc County. Layering represents repeated vol 
conic outbursts. Solid blocks of rock on quorry floor ond in quarry 
lace represent fragments of volcanic bombs. The cinders from this cone 
ore used for railroad construction. Observer faces north. Photo by 
Charles W. Chesfermon. 

The region's principal sources of sand and gravel 
are local stream alluvium in various localities; deltaic 
lake terrace deposits in Goose Lake, Surprise, and 
Honey Lake Valle\s, and in the Madeline Plains; and 
Quaternar>- flood-plain gravels near Aituras and 
Chester. 

Stone, Crushed 

Like sand and gravel, and volcanic cinders, crushed 
stone is produced and used throughout the region in 
undetermined tonnages, with almost all being used 
for asphalt concrete aggregate and road building ma- 
terial. X'arious Tertiary and Quaternary basalt and 
andesite flow s are sources of high-specification crushed 
stone throughout the region; notable quarries are at 
Canby Bridge and Likely, .Modoc County. Decom- 
posed granitic rock is quarried for road and fill pur- 
poses in Hone>' Lake \'alley, Lassen County, and else- 
where Tertiar\' andesitic tuff breccias and vent 
agglomerates are sources of crushed stone for road 
building uses. 



Stone. Dimension 

In the 1800's and early 1900's, small tonnages of 
Tertiary tuffs and tuff breccias near Aituras, .Modoc 
Count\, and Susanvillc, Lassen Counts', were quarried 
for local use in a few public and commercial buildings. 
None of these quarries has been active for several 
decades. 

Volcanic Cinders 

Cinder cones at about 20 localities in northeastern 
Shasta County, eastern Siski\-ou Countv, and western 
.Modoc County, have been sources of about 5 million 
tons of volcanic cinders since large-scale quarrying 
began in this area in the early 1930"s. Production from 
tiie region has been about 140,000 tons of volcanic 
cinders each \ear for the past decade — about two- 
thirds to three-fourths of California's annual produc- 
tion. 

The cinders at most cones are red, gra\', or black 
basaltic to andesitic scoria fragments. The cinders are 
layered as they originally fell and are accompanied 
h\ scattered \<jlcanic bombs. .Most of the cones that 
have yielded cinders are Pleistocene, but a few are 
Recent. 

Quarr\ing operations are t\ picall\' simple: After 
removal of thin overburden, the JooseK* consolidated 
cinders are scraped and loaded into trucks for the haul 
to market. Sometimes the raw cinders are screened to 
remove bombs and agglutinated clumps. The immense 
tonnages quarried for railroad ballast at Kegg, Siski- 
\ ou County, and East Sand Butte, .Modoc County, 
w ere loaded directly on railroad cars in the pits. 

The main tonnage of volcanic cinders from this re- 
gion has been used for railroad ballast, although this 
has been decreasing in the past decade; a les.ser but 
growing tonnage, from cones throughout the region, 
is used as road material — fill, asphaltic concrete aggre- 
gate, and surfacing material. Smaller tonnages, but also 
notablx' increasing over the past decade, are used as 
lightweight aggregate in building blocks: the cones 
at Hotlum, near Yreka, Siskiyou Count\-, and Poison 
Lake, near Susanville, Lassen Countw are the main 
sources of volcanic cinders used for building blocks. 



REFERENCES 



Averill, C. V., 1936, Minerol resources of Modoc County: 

Jour. Mines and Geology, v. 32, no. 4, p. 445-457. 
Averill, C. V., and Erwin, H. D., 1936, Minerol resources 

County: California Jour. Mines and Geology, v. 32, no. 4, p 
Chestermon, C. W., 1956, Pumice, pumicite, and volconic 

California: Colifornia Div. Mines Bull. 174, p. 3-97. 
Faick, J. H., 1963, Geology and technology of some natural 

in north^entral Californio: Econ. Geology, v. 58, no. 5, p. 
Hill, J. M., 1915, Some mining districts in northeostern Colifi 

northv»e$tern Nevada: U.S. Geo!. Survey Bull. 594, 200 p. 
Lydon, P. A., and O'Brien, J. C, 196 , Mines and mineral 

of Shasta County: Californio Div. Mines and Geology, Coi 

(In press) 
Ross, C. P., 1941, Some quicksilver prospects in adjacent 

Nevada, Colifornio, and Oregon: U.S. Geol. Survey Bl 

p. 23-37. 



of Lossen 
405-444 
cinders in 

pozzolans 
702-719. 
ornio and 

resources 
<nty Rept. 

ports of 
II. 931-B, 



Sofonov, Anotole, 1962, The Chollenge of the Socromento Valley, Coii 
fornio, in Bowen, O. E., ed.. Geologic guide to the gas ond oil 
fields of northern Colifornia: California Div. Mines ond Geology 
Bull. 181, p. 77-97. 

Stearns, N. D., Stearns, H. T., and Woring, G. A., 1937, Thermo.l 
springs in the United Stotes: U.S. Geol. Survey Woler-Supply Poper 
679-B, p. 59-206. 

Tucker, W. B., 1919, Lassen County and Modoc County: California Min. 
ing Bur., 15th Rept. State Mineralogist, pt. 2, chops. 2-3, p. 226-253. 

Waring, G. A., 1915, Springs of California: U.S. Geol. Survey Woter. 
Supply Paper 338, 410 p. 

White, D. E., 1955, Violent mud-volcano eruption of Lake City hot 
springs, northeastern Colifornia: Geol. Soc. America Bull., v. 66, 
no. 9, p. 1109-1130. 



CHAPTER IV 
SIERRA NEVADA PROVINCE 




Page 



107 Geology of the Sierra Nevada, by Paul C. Bateman and Clyde Wahrhaftig 

173 Geology of the Taylorsville area, northern Sierra Nevada, by Vernon E. McMath 

185 Tertiary and Quaternary geology of the northern Sierra Nevada, by Cordell 

Durrell 
199 Cenozoic volcanism of the central Sierra Nevada, by David B. Slemmons 
209 Economic mineral deposits of the Sierra Nevada, by William B. Clark 



[ic,-] 



IC 




Mount Lyell group, and the source of the Tuolumne River. From J. D. Whitney, The Yosemite GufdeBool, 1870. 



GEOLOGY OF THE SIERRA NEVADA 

By Paul C. Bateman and Clyde Wahrhaftig * 
U.S. Geological Survey, Menlo Park, California; 
U.S.G.S. AND University of California, Berkeley 



The Sierra Nevada is a strongly asymmetric moun- 
tain range with a long gentle \\estern slope and a high 
and steep eastern escarpment. It is 50 to 80 miles wide, 
and it runs west of north through eastern California 
for more than 400 miles — from the Mojave Desert on 
the south to the Cascade Range and the Modoc Plateau 
on the north (pi. 1). Mount Whitney, in the south- 
eastern part of the range, attains a height of 14,495 
feet and is the highest point in the conterminous 
United States. The "High Sierra," a spectacular span 
of the crestal region, which extends north from Mount 
Whitney for about a hundred miles, is a glaciated 
region characterized by numerous lakes and a proces- 
sion of 13,000- and 14,000-foot peaks. 

The range is a tremendous physical barrier to the 
passage of moisture eastward from the Pacific. Polar 
front cyclones expand adiabatically as the\' pass over 
the Sierra Nevada during the winter and cool well 
below their dewpoint. Most of the moisture that was 
obtained during the passage of warm air masses across 
the Pacific is precipitated as snow, which is preserved 
as a heavy snow pack at high altitudes and in the shade 
of the forests at lower elevations until late spring or 
summer. On the east side of the Sierra Nevada the de- 
scending air is warmed adiabatically and can hold more 
moisture than it contains. Hence the arid valleys of 
the Great Basin are "lands of little rain." 

But the Sierra Nevada is more than a physical and 
climatic barrier; until recently it has been a remark- 
ably effective barrier to geologic thought. Its tower- 
ing eastern escarpment has been a boundary for think- 
ing about problems in the Great Basin; and geologists 
working in the Great Valley, the Coast Ranges, or 
even along the west slope of the Sierra Nevada itself, 
have seldom looked eastward for correlations. Even 
now, we are only on the threshold of understanding 
the tremendous role the Sierra Nevada has played in 
the geologic history of the West. 

GENERAL GEOLOGIC RELATIONS 

The Sierra Nevada is a huge block of the earth's 
crust that has broken free on the east along the Sierra 
Nevada fault system and been tilted westward. It is 
overlapped on the west by sedimentary rocks of the 
Great Valley and on the north by volcanic sheets ex- 

* Publication authorized by the Director, U.S. Geological Survey. Bateman 
prepared the parts of the report that deal with the bedrock geology 
and Wahrhaftig the parts that deal with the Cenozoic geology. 



tending south from the Cascade Range. A blanket of 
volcanic material caps large areas in the north part of 
the range. 

Most of the south half of the Sierra Nevada and the 
eastern part of the north half are composed of plutonic 
(chiefly granitic) rocks of Mesozoic age. These rocks 
constitute the Sierra Nevada batholith, which is part 
of a more or less continuous belt of plutonic rocks that 
extends from Baja California northward through the 
Peninsular Ranges and the Mojave Desert, through the 
Sierra Nevada at an acute angle to the long axis of the 
range, and into western Nevada; it may continue at 
depth beneath the volcanic rocks of the Snake River 
Plains and connect with the Idaho batholith. 

In the north half of the range the batholith is flanked 
on the west by the western metamorphic belt, a ter- 
rane of strongly deformed and metamorphosed sedi- 
mentary and volcanic rocks of Paleozoic and Mesozoic 
age. The famed iVIother Lode passes through the heart 
of this belt. Farther south, scattered remnants of meta- 
morphic rock are found within the batholith, espe- 
cially in the western foothills and along the crest in 
the east-central Sierra Nevada. The batholith extends 
eastward to the east edge of the range, but in the south 
half of the range one can look eastward across Owens 
Valley to the wall rocks on the east side of the bath- 
olith making up the White and Inyo Mountains. 

The story of the Sierra Nevada is in four overlap- 
ping parts: (1) a long period in the Paleozoic when 
the area was mosth- under the sea receiving sediments; 
(2) a shorter period during the Mesozoic when the 
Paleozoic strata were downwarped into a gigantic 
complexly faulted synclinorium which was filled with 
contemporaneous volcanic and sedimentary detritus, 
strongly deformed, intruded repeatedly by granitic 
masses, and eroded to a depth of 9 to 17 miles; (3) a 
period of relative stability in the early Cenozoic; and 
(4) a period of uplift, tilting, and faulting, preceded 
and accompanied by volcanic activity, in the late 
Cenozoic. 

MILESTONES OF GEOLOGIC STUDY 

The early literature of the Sierra Nevada is replete 
with the names of geologic "greats" who were lured 
into attacking some of its vexing problems — names 
such as John Muir, J. D. Whitney, Clarence King, 
Joseph Le Conte, A. C. "Andy" Lawson, Adolph 
Knopf, Waldemar Lindgren, F. L. Ransome, W. H. 



[ 107] 



108 



Geology of Northkrn California 



Bull. 190 



Turner, and Francois Mattlics. The first geologic 
studies were begun a little more than a hundred years 
ago by the CJeological Survey of California, headed 
by J. D. Whitney. In the Sierra Nevada, geologists 
of the "\Vhitnc\- Survc>'" devoted their attentions 
chicfl\- to the "gold belt" of the metamorphic western 
foothills and to reconnaissance of the still largely un- 
known higher granitic countr\- to the east and south- 
east (Whitney, 1865). In 1886 Waldemar Lindgren 
and H. W. Turner, under the direction of G. F. 
Becker, were assigned by the U.S. Geological Survey 
to stud_\- the "gold belt," and between 1894 and 1900 
Lindgren and Turner, together with F. L. Ransome 
\\ho had joined them later, published 12 regular folios 
and I special folio, which together are known as the 
"gold belt" folios (Lindgren, Turner, and Ransome, 
1894-1900). In terms of the time expended in field- 
work and report preparation measured against mag- 
nitude and value, these folios are truly a remarkable 
achievement. The\' were followed, in 1911, by Lind- 
gren's report, "The Tertiary gravels of the Sierra 
Nevada." In 1915 Adolph Knopf undertook a study 
of the Mother Lode System (Knopf, 1929); in 1932 
H. G. Ferguson and R. W. Gannet published on the 
gold quartz veins of the Alleghany district; and in 
1940 W. D. Johnston published the results of a stud> 
of the Grass Valley gold district. 

These publications provided much information on 
the character and distribution of the rocks in the west- 
ern metamorphic belt, but the extremely comple.x 
stratigraphy and structure of the belt remained ob- 
scure. N. L. Taliaferro made some progress in un- 
raveling the structure and stratigraphy, chiefly by 
applying criteria indicating the top directions of beds 
(1943), and the continued use of these criteria to de- 
termine the order of superposition has been a principal 
tool in most subsequent work (Clark, 1964). Recentlx 
students at the University of California at Berkeley 
have applied statistical methods of structural analysis 
to .selected small areas (Parker, 1961; Baird, 1962; Best, 
1963; Christensen, 1963), and this technique also aids 
in building up a knowledge of the structure and stra- 
tigraphy. 

.Adolph Knopf's study in 1912 and 1913 of the east- 
ern Sierra Nevada and the Inyo Mountains (1918) was 
the first publication to deal with a large area of the 
Sierra Nevada batholith. F.ven though a reconnais- 
sance stud)', it showed that the batholith is composed 
of many separate granitic intrusive bodies and clearl\' 
pointed the wa\' for further work. I-"ven earlier, prob- 
ably prior to 1910, H. W. Turner had mapped parts 
of the Yoscmite and Mount L\ell 30-minute quad- 
rangles, which together span the batholith, but the 
mapping was never completed. Turner's maps did 
serve, however, as the start for a bedrock map of the 
Yosemite region that was prepared by F. C. Calkins 
( 1930) in connection w ith a study of its ph\siographic 
development by Francois Matthes. Calkins' map accu- 



rately shows the separate granitic intrusive rocks in 
the \'oscmitc region, and his brief accompanying text 
includes descriptions of field relations that establish 
the sequence of intrusion. This map served as the base 
for F.rnst Cloos' (1936) well-known stud>' of the pri- 
mar\- structures of the granitic rocks, "Der Sierra 
Nevada pluton," and also provided a test for age de- 
terminations of rocks by the potassiuni-argf)n (K-.-\r) 
method (Curtis and others, 1958). 

In 1934 K. B. Ma\() published tiie results of studies 
in the Laurel and Convict Basins of the eastern Sierra 
Nevada, and in 1937, 1941, and 1947 he published the 
results of reconnaissance structural studies of the gra- 
nitic rocks of the eastern Sierra Nevada. 

Ju.st before World War II, Durrell (1940) and 
Macdonald (1941) published reports that deal with 
sizeable areas in the western foothills south of the 
w estern metamorphic belt. These authors were con- 
cerned primariK' with the structure and metamor- 
phism of the metamorphic rocks, but also made an 
effort to distinguish the different granitic rocks. About 
the same time. Miller and Webb (1940) published a 
map and description of the Kernville 30-minute quad- 
rangle in the southern part of the Sierra Nevada. 
Somewhat later Ross ( 1958) published a report on the 
bedrock geology of a part of Sequoia National Park, 
and Hamilton (1956a, 1956b) published the results of 
studies in the Huntington Lake area of the central 
Sierra Nevada. 

During World War II, geologists of the U.S. Geo- 
logical Survey investigated the tungsten deposits of the 
Sierra Nevada, and at the end of the war undertook 
regional studies of some of the more productive areas 
in the central Sierra Nevada. Noteworth\- reports and 
maps dealing with the geology of the central part of 
the range are those of Krau.skopf, 1953; Rinehart and 
Ros.s, 1957, 1964; Bateman, 1956, 1965; Moore, 1963. 
In 1963 the geologists of the U.S. Geological Survey 
then working in the Sierra Nevada published a syn- 
thesis of the gcolog\ of the central part of the Sierra 
Nevada batholith between parallels lat 36°45' and 
3800' N.. where the Survey has made most of its 
studies and is continuing its investigations (Bateman 
and others, 1963). This report includes documentation 
supporting the hypothesis held by nian\' geologists that 
the batholith is intruded into the axial region of a 
s\ nclinorium. Important studies of the satellitic intru- 
sive bodies in the w estern metamorphic belt have been 
made by Hietenan (1951), Compton (1955), and Best 
(1963). Studies of the Sierra Nevada made since the 
late 1950's have been aided by the new methods of 
dating granitic and volcanic rocks isotopicall\- (Curtis 
and others, 1958; Kistler and others, 1965; Hurley and 
others, 1965). 

The study of the Cenozoic rocks of the Sierra 
Nevada began at an early date for the practical reason 
that the gold-bearing gravels in the stream beds and 
on interstream divides are of Cenozoic age. The flood 



1966 



Batkman AM) Wahrhaftig: Sikrra Nkvada 



109 



of miners during the Gold Rush of 1849 quicklv ex- 
hausted the rich placers along the riverbeds and spread 
over the flat ridgetops, where high grav^els were found 
and prospected. As earl\- as 1849, P. T. Tyson, a geo- 
logical traveler, inferred from these high gravels 2,000 
feet of Tertiary uplift in the Sierra Nevada (Whitnev, 
1880, p. 66). ]. B. Trask, AI. D., the first State Geolo- 
gist, in a report published in 1853, described the min- 
ing of these high bench gravels and deduced from 
their distribution that they had been deposited by an 
ancient stream flo\\ing northward athwart the present 
drainage. 

Mining of these bench gravels was probably the 
major industry of the State during the latter decades 
of the 19th century. The gravels were mined by two 
methods. Where exposed they were "hydraulicked" 
by playing jets of water under high pressure upon the 
gravel banks and washing the dislodged material 
through sluice boxes, where the gold was trapped on 
riffles and the waste was discharged into the present 
stream beds. Where thick volcanic overburden made 
hydraulicking impracticable, mining was conducted by 
driving horizontal tunnels, called drifts, through the 
gold-bearing gravel at the base of the channels. Need- 
less to say, the ability to predict the course and slope 
of the gravel channels, and particularly' of the gold- 
bearing "leads" at the base of the gravels, was of im- 
mense importance to the miners, and the scientific 
study of the auriferous gravels began early. This 
study was promoted, in turn, by the great \\ealth of 
exposures and information that was made available as 
the hydraulic mines ate away at the banks of gravel, 
exposing the ancient river beds, and as the drift mines 
explored the courses of the ancient rivers beneath 
their volcanic cover. In the areas downstream from the 
mines the hydraulic operation was immenseh' destruc- 
tive of agricultural land and navigable channels, be- 
cause of the vast quantities of gravel that were poured 
into the river systems; and hydraulicking was greatly 
curtailed by court action in 1884 and virtually ceased 
by 1905. Drift mining has been carried on sporadicall\' 
until recent years, but its heyday of activity was the 
latter part of the 19th century. 

The first great summary of the geology of the aurif- 
erous gravels was that of J. D. Whitney (1880) and 
was based largely on the investigations of the Whitney 
Survey of 1860 to 1874, although 2 years earlier Leo 
Lesquereux (1878) had published the results of his 
monumental study of the fossil plants of the auriferous 
gravels. Whitney's report contains a \\ealth of infor- 
mation on the distribution and character of the gravels 
as exposed up to that time, and also an extended dis- 
cussion of the Calaveras skull, which was then regarded 
as the most convincing evidence for the existence of 
"Pliocene Man" in North America. 

Joseph Le Conte (1880, 1886) concluded that the 
auriferous gravels indicated that the Sierra Nevada had 
been uplifted and titlted westward, while Whitney 



(1880, p. 317) contended that the Sierra had not been 
uplifted since the gravels were deposited. Ross E. 
Browne (1890) attempted the first scientific test of 
Whitney's and Le Conte's opposed theories by making 
a careful stud\' of the auriferous gravels of the Forest 
Hill Divide and comparing the gradients of the vari- 
ously- directed segments of the ancient streambeds. 
Within the limits of error of the scanty information 
then available, he could find no significant difference 
in the slopes of the stream segments that trended in 
different directions, and he concluded, reasonably 
enough, that there had been no tilting of the Sierra 
Nevada since the gravels were deposited! 

The SNStematic geologic mapping of the Gold Belt 
by Lindgren, Turner, and Ransome of the U.S. Geo- 
logical Surve\', between 1886 and 1900, included a 
study of the distribution and character of the Tertiary 
gravels and the volcanic rocks that overlie them. 
Lindgren's (1911) paper on the Tertiary gravels of the 
Sierra Nevada is still the standard \\ ork on Cenozoic 
history of the northern part of the range. An interest- 
ing sidelight of this paper is the final disposal of the 
question of the Calaveras skull, which had been caus- 
ing controversy ever since it was discovered (Bret 
Harte, 1887). One of Lindgren's assistants, J. .M. Bout- 
well, made a special trip to the discovery site and 
obtained from one of the original perpetrators the 
confession that it was a practical joke played upon a 
local physician and amateur scientist, thus confirming 
Bret Harte's estimate of the situation. 

Since Lindgren's day, little geologic work has been 
done on the auriferous gravels, although the forma- 
tions along the west edge of the foothills, into which 
the gravels are thought to grade, have been studied 
by Dickerson (1916), Allen (1929), Clark and Ander- 
son (1938), and Creely (1955). The fossil floras from 
the gravels, originally studied by Lesquereux and 
Knowlton in collections whose stratigraphic relations 
were uncertain, have been recollected and restudied 
by Potbury (1937), MacGinitie ( 1941 ), Condit ( 1944a, 
1944b) and A.xelrod (1944). The few vertebrate re- 
mains that have been found have been studied by 
Wood (1960), VanderHoof (1933), and Stirton and 
Goeriz (1942). 

Hard volcanic debris (generally rhyolitic ash flows 
and andesitic mudflows) that overlies and locally cuts 
ofi^ the auriferous channel gravels was called by the 
miners "cement" or "cement rock," but its volcanic 
origin was earl\' recognized. Lava flows intercalated 
\\ ith the andesitic mudflows formed sinuous table 
mountains that excited the admiration of early Cali- 
fornia travelers and were described extensively in 
Whitney's reports. Between 1886 and 1900 Turner 
and Ransome did much petrographic work on the 
Cenozoic volcanic rocks, Ransome ( 1898) coining the 
term "latite" to describe the rocks of the Stanislaus 
Table Mountain. The volcanic formations of the 
northern Sierra Nevada were named by Piper and 
others (1939) and have been the subject of investiga- 



no 



Gkology ok Northern California 



Bull. 190 



tion 1)\ Diirrcli (iV5y), Curtis (1954), Wilshirc 
(1957),' ;ind SIcmnions (195.^). Ciiibcrt (1938, 1941) 
has investigated Upper Ceno/.oic volcanic rocks on the 
east side of the Sierra Nevada south of Mono Lake, 
and Thompson and White ( 1964) and Birkeland 
(1963) have investigated similar rocks north of Lake 
Tahoe. 

Glaciation of the Sierra Nevada was recognized as 
earlv as 1S63 by J. D. Whitney; shortly thereafter 
Clarence King and J. T. Gardiner, w iio were then also 
with the Whitney Survc\', recognized extensive evi- 
dence of glaciation near Yoscniite \'alley. Both Whit- 
ney and King, however, maintained that the vaile\' 
was structural in origin and not the result of glacial 
erosion. John .Muir published in 1K72, 1874, and 1880 
a vivid account of the evidence for a glacial origin of 
Voscmite \'allcy (Colby, 1950), and Jo.scph Le Conte 
(1873) described evidence for glaciation in the north- 
ern Sierra Nevada. 

I. C. Russell (1889 )described the Quaternary his- 
tory of the Mono Basin, and showed that the existing 
glaciers arc not shrunken remnants of the Pleistocene 
ice sheets but formed after a period of complete dis- 
appearance of the ice. Glacial deposits are shown on 
the U.S. Geological Surve\' folios published between 
1896 and 1900. H. W. Turner, in 1900, published a 
report on the Pleistocene geology of part of the Sierra 
Nevada, in which he concluded that Yosemite X'alley 
is a river valley controlled by jointing but somewhat 
modified b\- ice. He also showed that there had been 
two periods of glaciation in the Sierra Nevada, sep- 
arated by a long interglacial period. In 1904 A. C. 
Lawson mapped the extent of glaciers in the upper 
Kern Basin, and between 1905 and 1907 W. D. John- 
ston, u ho had been Russell's topographer, recognized 
in the Walker River drainage three glacial advances. 

Modern work on the glacial geology of the Sierra 
Nevada began w ith the studies of Francois E. Matthes 
(1930, 1960, 1965) and Eliot Blackwelder (1931). 
Blackwelder recognized four glacial stages on the east 
side of the Sierra, and Matthes recognized three on the 
west side; although the\- consulted frequently in the 
field, thev were unable to agree on a correlation across 
the Sierra Nevada. Later, W. C. Putnam mapped the 
moraines in the Mono Basin (1949, 1950) and the 
Rock Creek-McGee Mountain area (1960a, 1960b, 
1962). 

Birman ( 1954, 1964) traced glacial deposits from 
the upper San Joa(iuin on the west side of the range 
to Rock (]reck on the east side, establishing a correla- 
tion. Sharp and Birman ( 1963) refined the later history 
of glaciation, adding two new glaciations. Sub- 
division along the east margin of the San Joaquin \'al- 
ie\' using soil-stratigraphic techniques on the alluvium, 
which is largel\' of glacial outwash origin, promises to 
'give a complete sequence of glaciations on the west 
side (Davis and Hall, 1959; .\rkley, 1962a, 1962b; 
Janda, 1965a, 1965b). 

The glacial chronolog\- of the Truckee area has 
been mapped by Birkeland (1964) who also effected 



a tic with the lake stratigraphy of the Lahontan Basin 
by tracing catastrophic flood deposits from Lake Ta- 
hoe down the Truckee River can\'on (1965). 

Investigation of glacial geology is being continued 
by Birkeland in the Tahoe area, Malcolm Clark in the 
West Walker Basin, R. P. Sharp along the east side 
of the Sierra Nevada south of Bridgeport, R. J. Janda 
in the San Joaquin Basin, and J. H. Birman in Sequoia 
National Park. 

The amount and time of uplift and tilting of the 
Sierra Nevada, and the date of the eastern boundary 
faulting, have been under investigation since the early 
work on the problem by Whitney, King, and Le 
Contc. In his 1911 paper, Lindgren summarized the 
evidence for uplift and tilting, and Louderback ( 1924) 
placed this uplift in late Pliocene time. Hudson (1955, 
1960) questioned Lindgren's main conclusion — that the 
Sierra has been tilted as though it was a rigid block — 
and by his own method of calculation arrived at an 
amount of uplift much less than that of Lindgren. 
.•Xxelrod (1957), from a study of the floras on 
the east side of the Sierra, concluded that in earh' 
Pliocene time the range could have been no higher 
than Lindgren claimed. The evidence for tilting in the 
Sierra Nevada has recently been reviewed by Chris- 
tensen (1966) who also agrees with Lindgren. 

As the auriferous gravels and extensive volcanic 
deposits are lacking in the Sierra Nevada south of the 
Tuolumne, geologists in the southern area have had 
to rel\- on physiographic c\idence of uplift. A. C. 
Lawson (1904) recognized three stages of uplift and 
partial peneplanation in the Kern Can\on region. 
Knopf (1918) traced the ancient erosion surfaces rec- 
ognized 1)\ Lawson northward along the east side of 
the range. Matthes (1930) found evidence for three 
stages of uplift and erosion in the Yosemite region and 
traced these into the San Joaquin drainage (Matthes, 
1960). He also added to the erosion .surfaces recog- 
nized bv Lawson in the Whitney area (Matthes, 1937, 
1965). Webb (1946) showed that the Kern Canyon 
fault had not been active in late Ccnozoic time, .\xel- 
rod ( 1962; Axclrod and Ting, 1961) attempted to date 
the erosion surfaces in the Sierra Nevada by study of 
pollen-bearing sediments on them. Recently the valid- 
it\ of summit flats, benches, and nickpoints on stream 
profiles, as indicators of former base level and uplift, 
has been challenged b>- Wahrhaftig (1965e) who 
believes the\- can form in granitic terrane at any alti- 
tude independent of regional base level. 

In the past few years, two techniques of dating and 
correlation have been applied to the volcanic rocks 
of the Sierra Nevada: potassium-argon dating (Evern- 
den, Curtis, and Kistler, 1957; Dalrymple, 1963, 1964a, 
1964b; lAcrnden, Savage. Curti.s, and James, 1964; 
Dalrymple, Cox, and Doell, 1965), and dating by 
means of identification of the geomagnetic polarity 
epoch.s, which consist of intervals of about 0.7-1.5 
million years during w hich the polarity of the earth's 
magnetic field was either as it is now (normal) or 



1966 



Batf.man and VVahrhaftic;: Sikrra Nfxada 



111 



\ 



reversed (Doell, Dalr\'mple, and Cox, 1966). Used 
together to check each other, and as an extension of 
the costly potassium-argon dating by the relatively 
cheap paleomagnetic method, these techniques are pro- 
viding new insights into the age of uplift and down- 
cutting, the time of glaciation, and the nature of the 
deformation in the Sierra Nevada during Cenozoic 
time. 

Interest in the crustal structure beneath the Sierra 
Nevada began in 1936 when Lawson published a paper 
"The Sierra Nevada in the light of isostasy." In a com- 
ment on Lawson's paper, B\erly (1938) inferred a 
root beneath the Sierra Nevada from dela_\' in the 
arrival time at stations east of the range in response to 
earthquake waves that originated west and northwest 
of the range. Eaton (1963, p. 5805) has made seismic 
refraction measurements across the northern part of 
the range that indicate this root ma\- extend to a depth 
of about 45 km near Lake Tahoe, and Eaton and 
Healy (1963) have made similar measurements across 
the high central part that indicate the root here ex- 
tends to depths of at least 50 km. iMikumo ( 1965) has 
confirmed the existence and approximate depth of the 
root. 

Extensive gravit\' measurements reported bv Oliver 
(1960, 1965), Oliver and Mabey (1963), and Oliver, 
Pakiser, and Kane (1961) show eastward decrease in 
Bouguer gravit\ values by larger amounts than clas- 
sical treatment of the data requires for isostatic equi- 
librium; part, and perhaps all, of the excess decrease 
reflects eastward decrease in the average density of 
the surface rocks. 

Pakiser, Press, and Kane (1960) have investigated 
the structure of the Mono Basin east of the Sierra 
Nevada using gravimetric, magnetic, and seismic tech- 
niques, and Pakiser, Kane, and Jackson ( 1964) have 
similarly investigated the subsurface structure of the 
Owens V^alley region. In 1964 Thompson and Talwani 
published two papers in which they presented an in- 
terpretation of the subcrustal structure of the Sierra 
Nevada and bordering regions. 

Aeromagnetic maps of part of the western meta- 
morphic belt (Henderson and Bass, 1953) and of 
Long Valley and northern Owens \'alle\' ( Henderson, 
White, and others, 1963) have been published, and 
others have been made but not published. 

Wollenberg and Smith ( 1964) have begun stud\- of 
the distribution of uranium, thorium, and potassium in 
the granitic rocks of the central Sierra Nevada, in order 
to determine the radiogenic heat yield of the surface 
rocks. In 1964 and 1965 several borings to measure 
heat flow were made by investigators of the U.S. 
Geological Survey and Harvard University, but none 
of the results was published by the end of 1965. 

PREBATHOLITHIC "FRAMEWORK" ROCKS 

The Sierra Nevada batholith was intruded into a 
framework of Paleozoic and early Alesozoic strata 
which are preserved in the walls of the batholith and 
in roof pendants, septa, and inclusions within the bath- 



olith (pi. 1). The rocks that form the west wall of 
the batholith are exposed in the western metamorphic 
belt, but the cast contact of the batholith is hidden 
beneath surficial deposits of Cenozoic age. However, 
the composition, structure, and age of the eastern wall 
rocks are shown in a narrow belt of roof pendants 
that extends southeast from Bridgeport to Independ- 
ence and in the White and Inyo (Mountains east of 
Ow ens Valley. The Paleozoic strata indicate a transi- 
tion from miogeosynclinal facies east of the batholith 
to eugeosynclinal facies west of the batholith. Most 
of the Mesozoic strata are eugeosynclinal, but a belt 
of roof pendants of possible Triassic age extending 
southeast from Huntington Lake contains miogeo- 
s\nclinal strata (fig. 1). 

Paleozoic Rocks 

All the Paleozoic systems are represented in the 
White and Inyo Mountains east of the Sierra Nevada. 
There, 26,000 feet of fossiliferous strata of Paleozoic 
age rest with structural conformity on 13,000 feet of 
strata that have \ielded no fossils and are presumed to 
be of late Precambrian age. The upper Precambrian 
and Lower Cambrian strata are composed of fine clas- 
tic sediments and carbonate rocks, chiefly dolomite in 
the Precambrian and limestone in the Lower Cam- 
brian. The Paleozoic strata of Aliddle Cambrian and 
younger age are dominantl\' carbonate in the southern 
Inyo Mountains, but include some quartzite, siltstone, 
and shale. Northward the amount of siliceous and ar- 
gillaceous clastic material increases, and the amount of 
carbonate decreases, particularly in the Mississipian 
and Pennsylvania strata. 

Paleozoic rocks in the roof pendants of the eastern 
Sierra Nevada contain much smaller amounts of car- 
bonate rock than those of the White and Inyo Moun- 
tains. They consist largely of fine-grained, thin-bedded 
siliceous hornfelses derived from siltstone, mudstone, 
and shale. Interbedded with the siliceous hornfelses are 
subordinate amounts of metamorphosed limestone, 
orthoquartzite that is locally calcareous, chert, and 
calcareous or dolomitic siltstone. The most complete 
Paleozoic section in the eastern Sierra Nevada is in the 
iMount Morrison roof pendant (fig. 1) and is more 
than 32,000 feet thick (Rinehart and Ross, 1964, p. 1). 
The lower part of the sequence contains fossils of 
Early to Middle or Late Ordovician age and consists 
of 19,100 feet of alternating thin-bedded siliceous and 
pelitic hornfels, marble, slate, metacheri, and thick- 
bedded calcareous orthoquartzite. An upper part that 
contains fossils of Penns\lvanian and Permian(?) age 
consists of about 7,300 feet of siliceous hornfels and 
some limestone. 

Through most of the length of the western meta- 
morphic belt. Paleozoic strata occupy the eastern part 
of the belt and lie adjacent to the batholith, but north 
of lat 39° N. a narrow strip of Mesozoic strata lies be- 
tween the Paleozoic strata and the batholith. The Pale- 
ozoic strata are generally in fault contact on the west 



1966 



5atk.man AM) W'AMRiiAFrui: Surra Niaada 



113 



y. 



with IMesozoic strata. The Melones fault zone (Clark, 
1964, p. 7) is the bounding structure in the south half 
of the belt, and a westerly branching strand of that 
fault is the bounding structure in the north half. 

Most of the Paleozoic strata in the western nieta- 
morphic belt have been referred to the Calaveras For- 
mation, which contains sparse fossils of Permian age 
in its upper part but which is predominantly unfossil- 
iferous. In the Ta\lorsville region at the north end of 
the belt, Diller ( 1908) divided the Paleozoic strata into 
11 formations, and iMcMath in the following article in 
this bulletin has recognized 8 formations above a 
thrust fault and 5 formations below, 4 of which are the 
same as those above the thrust. Fossils of Permian and 
Early Alississippian age have been collected from 
these rocks, and the stratigraphically lowest formation, 
the Shoo Fl\' Formation, is believed to be, at least in 
part, of Silurian(?) age (Clark and others, 1962). Far- 
ther south, in the vicinity of the American River, Lind- 
gren (1900) divided the Paleozoic strata into five 
formations. Clark and others (1962) abandoned Lind- 
grens Blue Canyon Formation reassigning its rocks to 
the Shoo Fl}- Formation as defined in the Taylorsville 
area. 

In the southern part of the western metamorphic 
belt, the most extensive Paleozoic rocks are black car- 
bonaceous phyllite and schist with thinly interbedded 
chert, but lenses of mafic volcanic rocks and limestone 
are widespread and localh' attain thicknesses of several 
thousand feet. In the northern part of the region, mafic 
volcanic rocks, slate, and sandstone constitute about 
equal parts of the Paleozoic section. 

Mesozoic Stratified Roclcs 

Strata of Mesozoic age crop out in several north- 
west-trending belts that parallel the long axis of the 
batholith and the regional grain. In the eastern Sierra 
Nevada a group of roof pendants that contain iMes- 
ozoic strata extends for more than 150 miles. In the 
western metamorphic belt the most extensive Alesozoic 
strata lie along the west side, west of the Paleozoic 
strata, but a shorter and narrower strip lies between 
the north half of the strip of Paleozoic strata and the 
Sierra Nevada batholith. In addition, at least part of 
the miogeosynclinal strata in roof pendants that ex- 
tend from near Huntington Lake for about 65 miles 
southeast through the heart of the batholith may be 
of Mesozoic age. 

The Mesozoic strata in the belt of pendants through 
the east side of the batholith consist chiefly of meta- 
volcanic rocks and graywacke-t\pe sedimentar\' rocks 
that were derived chiefly from the volcanic rocks. 
These rocks weather gray and contrast strongly with 
the nearby hornfelsed miogeos\'nclinal Paleozoic strata, 
which weather reddish brown. Pyroclastic rocks of 
felsic to intermediate composition, which are the most 
common rocks, are interlayered with mafic flows and 
cut by hypabyssal intrusives. Thin beds of epiclastic 
rocks are sporadically scattered throughout the meta- 



volcanic sequence. The thickest section of .Vlesozoic 
strata in the eastern Sierra Nevada is exposed in the 
Ritter Range roof pendant where about 30,000 feet of 
metamorphosed pyroclastic rocks of intermediate to 
felsic composition stratigraphically overlie rocks of 
Paleozoic age (Huber and Rinehart, 1965). 
The presence of graded beds, crossbeds, limestone 
lenses, ashflow tuffs, and accretionar\' lapilli indicates 
varied environments of deposition, including both sub- 
aqueous and subacrial. Earl\- Jurassic fossils have been 
collected from a localit\' about 10,000 feet stratigraph- 
icall\- above the lower contact with Paleozoic rocks. 
Middle or Upper Jurassic or even Cretaceous .strata may 
be present in the 20,000 feet of unfossiliferous strata 
that overlie the fossiliferous zone. A Permian age of 
230 to 265 million years by the rubidium-strontium 
whole-rock method of age dating was reported b\- 
C. E. Hedge (U.S. Geol. Survey Prof. Paper 50 i, 
1964, p. A114) for strongK- foliated volcanic strata 
beneath the fossil zone; it suggests that Triassic rocks 
may be missing in this sequence and that volcanism 
may have begun before the end of the Paleozoic. 
However, in the southern Inyo Mountains about 1,800 
feet of fossiliferous marine limestone and shale of me- 
dial Early to earliest Middle Triassic (early Anisian) 
age are overlain, possibly unconformably, by unfos- 
siliferous interbedded continental volcanic and sedi- 
mentary strata that probably have a thickness in excess 
of 6,000 feet (A4erriam, 1963, p. 28-31; N. J. Silber- 
ling, written communication, 1962), showing that vol- 
canism did not begin there until Middle Triassic at 
the earliest. 

All of the Mesozoic strata of the western metamor- 
phic belt appear to have been deposited in a marine 
environment. The Mesozoic strata contain volcanics, 
as do the Paleozoic, and the differences between the 
rocks of the tv\o systems are much less conspicuous 
here than in the roof pendants of the eastern Sierra 
Nevada. Both Triassic and Jurassic fossils have been 
collected from the western metamorphic belt, but Ju- 
rassic fossils are more common, and Jurassic strata are 
far more widespread than Triassic. The extensive belt 
of Mesozoic strata along the west side of the western 
metamorphic belt has \ielded only Late Jurassic fossils, 
and the strata are generally considered to be restricted 
to the Late Jurassic (Clark, 1964, p. 15-31), although 
Eric and others (1955) and Taliaferro (1943) have 
allowed for the possibilit>' that the Logtown Ridge 
and Cosumnes Formations, which constitute the Ama- 
dor Group, may be in part of Middle Jurassic age. 
The belt includes .sequences of epiclastic rocks, largely 
slate, gravwacke, and conglomerate, commonly inter- 
bedded with volcanic rocks and in some places inter- 
tonguing with them. The gra\'wacke and conglom- 
erate of all formations arc similar in composition; the 
most abundant clasts are volcanic rocks, slate, and 
chert, but fragments of metamorphic rocks, plutonic 
rocks, and quartzite are widespread. The various 



114 



Gkology of Northirn California 



Bull. 190 




Photo 1. The metamorphosed strata of the Sierra Nevodo are complexly folded. A (obove)- 
Gently plunging fold in hornfels and marble. B (below)-Chevron folds in tufFoceous slate. 




1966 



Bateman and VVahrhaftig: Sierra Nevada 



115 



volcanic formations also have many features in 
common; most are composed largely of andesitic(r) 
tuff and volcanic breccia, but basaltic lavas, in part 
having pillow structure, form thick sequences locally. 
Felsic volcanic rocks, such as occur in the Mesozoic 
of the eastern Sierra Nevada, are found locally but 
are uncommon. 

In the Taylorsville region at the north end of the 
western metamorphic belt Upper Triassic strata are 
present (Diller, 1908), and, farther south at the Amer- 
ican River, a lens of probable Triassic strata uncon- 
formably overlies the Shoo Fly Formation of Silu- 
rian(?) age and is unconformably overlain by the 
Sailor Canyon Formation of Early and Middle Jurassic 
age (Clark and others, 1962). The Upper Triassic 
strata of the Taylorsville region (Diller, 1908) con- 
sists of two formations, the Hosselkus Limestone and 
the Swearinger Slate, with a combined thickness of 
about 1,100 feet, according to McMath (this bulletin). 
Early to Late Jurassic marine strata of Mount Jura in 
the Taylorsville region have been divided by Crick- 
may (1933) into 14 formations with a combined thick- 
ness of about 13,000 feet. Farther south, in the vicinit_\' 
of the American River, the Lower and Middle Jurassic 
Sailor Canyon Formation consists of at least 10,000 
feet of graywacke, andesitic(?) tuff, and siltstone. 

Structure of the "Framework" Rocks 

The Paleozoic and Mesozoic strata of the Sierra 
Nevada have been complexly folded and faulted, and 
beds, cleavage, and lineations, including fold axes, are 
commonly steep or vertical (photo 1 ). A predominance 
of opposing, inward-facing top directions in the strata 
on the two sides of the range define a complexly 
faulted synclinorium. This synclinorium is not readily 
apparent in the patterns of geologic maps chiefly be- 
cause strike faults of large displacement interrupt the 
sequence of strata in the western metamorphic belt. 
Apparently the axis of the synclinorium lies between 
miogeosynclinal Paleozoic strata on the east and eugeo- 
synclinal strata on the west. The axial part of the 
synclinorium is occupied by the granitic rocks of the 
Sierra Nevada batholith. It trends N, 40° W. in the 
central Sierra Nevada, but probably bends to north- 
ward in the northern Sierra Nevada. The east side of 
the batholith follows approximately the east side of 
the volcanogenic and epiclastic Triassic and Jurassic 
strata. The eastern limit of the synclinorium is marked 
by a belt of Precambrian and Cambrian rocks that 
extends from the White Mountains southeastward into 
the Death Valley region and beyond. The western 
limit presumably lies beneath the Cretaceous and Ter- 
tiary strata of the Great Valley. An interesting specu- 
lation is that the sharply arcuate pattern of outcrops 
of Precambrian rock along the east and south sides of 
the Mojave Desert (pi. 1) may result from a south- 
eastward continuation of the synclinorium. 

From the belt of older rocks that extends between 
the White Mountains and Death Valley, the strata on 



the east side of the batholith are progressively younger 
westward. The range-front faults that bound Owens 
Valley and the east side of the central Sierra Nevada 
strike obliquely across the major structures in these 
Paleozoic and Mesozoic strata. The strata east of the 
White and Inyo Mountains, and in many remnants 
within the Sierra Nevada batholith, are strongly folded 
and faulted, causing repetitions of formations, but in 
the Mount Morrison and Ritter Range pendants of the 
eastern Sierra Nevada the gross structure is homo- 
clinal, and bedding tops face west across more than 
50,000 feet of vertical or steeply dipping strata rang- 
ing in age from Ordovician to Jurassic. Folds in the 
western part of the Ritter Range pendant may be 
related to the axial region of the synclinorium. 

In the western metamorphic belt the gross distribu- 
tion of strata resulting from the development of the 
synclinorium has been reversed by movement along 
steeply dipping fault zones of large displacement, and 
the Paleozoic strata lie between two belts of Meso- 
zoic strata (see pi. 1). The internal structure of in- 
dividual fault blocks is, in general, homoclinal, and 
most bedding tops face east; the dip of the beds is 
generally more than 60° eastward (Clark, 1964, p. 
44). The homoclinal structure is interrupted in parts 
of the belt by both isoclinal and open folds, but the 
east limbs of anticlines commonly are longer than the 
west limbs, and the older strata in a fault block gen- 
erally are exposed near its west side and the younger 
strata near its east side. 

Unconformities have been recognized both within 
and between the Paleozoic and Mesozoic units, and 
they indicate repeated movement since middle Pale- 
ozoic time. The geometry of the structures of the 
"framework" rocks also indicates that the strata have 
been deformed either during several different episodes 
or during a single complex episode. Minor folds with 
steeply dipping axes are common and represent either 
refolding of earlier folds that were initially formed 
with subhorizontal axes or else folds that were formed 
in strata that had been previously so folded as to have 
steep dips. Some terranes contain two or more axial 
surfaces of systematically different orientation. 

The Sierra Nevada lies within the Cordilleran mo- 
bile belt and its rocks reflect part of the deformation 
that has taken place there since mid-Paleozoic time. 
Probably the faulted s_\'nclinorium began to take form 
in Permian or Triassic time, and intermittent disturb- 
ances occurred through the Jurassic. The very severe 
disturbance that took place near the close of the 
Jurassic and caused the principal folds in the Upper 
Jurassic strata of the western metamorphic belt is re- 
ferred to as the Nevadan orogeny, but both earlier and 
later disturbances are known to have occurred. Un- 
conformities in the Taylorsville region indicate dis- 
turbances between the Silurian and Mississippian, and 
at the end of the Permian, Triassic, and Jurassic (Mc- 
Math, this bulletin); and, in the eastern and central 
parts of the range, folds of two periods of deforma- 



116 



Gf.oi.ogy of N'orihkrn California 



Bull. 190 




Photo 2. Contact between por- 
phyritic and equigronulor quartz 



A 



rion antedate a third set that appears to have been 
formed during the Late Jurassic Nevadan orogeny. 
Kistler (in press) believes the earlier deformations 
occurred during the Late Permian and in the Early or 
.Middle Triassic. In the western nietamorphic belt, 
Clark ( 1964, p. 44) has recognized a stage of deforma- 
tion that occurred after the principal folding of the 
Upper Jurassic strata. This deformation is character- 
ized by the development of slip cleavage, steeply dip- 
ping minor folds, and steepl\- dipping lineations. Clark 
believes the large faults in the western nietamorphic 
belt formed during this deformation, probably by 
strike-slip movement. The presence of ultramafic 
rocks, especiall\' serpentine, along these faults suggests 
deep penetration, possibl\- penetration into the upper 
mantle. 

The major deformation of the stratified rocks took 
place in parts of the range before the emplacement of 
the adjacent plutonic rocks, but locall\- plutons have 
been affected b\" regional deformation, indicating an 
<)\crlap of the period of regional deformation with 
that of magma emplacement. For example, in the God- 
dard roof pendant of the cast-central Sierra Nevada 
(fig. 1), a second deformation of the nietamorphic 
rocks has affected plutons that were intruded after the 
first deformation. Farther west the eastern margin of 
the granodiorite of "Dinke\' Creek" type, one of the 
largest plutons in the western Sierra Nevada, was in- 
tensely sheared and lineated before the emplacement 
of the .Mount Givcns Granodiorite which is the larg- 
est pluton in the central part of the range. Some of 
the plutons w ithin the western nietamorphic belt also 
were sheared during the second deformation. 

The strata in the western nietamorphic belt, except 
where adjacent to the batholith or smaller intrusive 
bodies, exhibit green.schist facies regional metamor- 
phism. East of the batholith, in the White and Inyo 



.Mountains, the only evidence of regional metamor- 
phism is the presence of slaty cleavage in some pelitic 
and calcareous rocks. The strata adjacent to intrusive 
bodies and in remnants within the batholith are chiefi\' 
in the hornblende hornfels facies of contact metamor- 
phism, although in the inner aureoles of some plutons 
that were intruded at unusually high temperatures the 
minerals sillimanite and brucite indicate the ne.xt 
higher pyroxene hornfels facies. 

THE BATHOLITH 

The batholith has been studied most intensively 
across the central part, between the 37th and 38th 
parallels of latitude (fig. 1 ), and much of the following 
discussion pertains specifically to that area (Bate- 
man and others, 1963). However, the rest of the bath- 
olith appears to be very similar. The batholith is com- 
posed chiefly of quartz-bearing granitic rocks ranging 
in composition from quartz diorite to alaskite, bur 
includes scattered smaller masses of darker and older 
plutonic rocks and remnants of metamorphosed scch- 
mcntar\- and volcanic rocks. Rocks in the composi- 
tional range of quartz monzonite and granodiorite pre- 
dominate and are about equally abundant. 

Mafic Rocks 

The oldest and most mafic rocks of the batholith are 
small bodies of diorite, quartz diorite, and hornblende 
gabbro, which have been aptU called by iMayo (1941, 
p. 1010) "ba.sic forerunners" or simply "forerunners." 
Their distribution is reminiscent of the nietamorphic 
rocks, for the\ occur as small inclusions of small roof 
pendants within individual plutons or more silicic rock 
or as septa between plutons. Commonly the>' are asso- 
ciated w ith nietamorphic rocks, and many are crowded 
w ith nietamorphic inclusions. This intimate association 
with the nietamorphic rocks probably results from the 



1966 



BaTF.MAN and WaHRHAFTIC;: SiKRRA NlAADA 



117 



mafic plutonic rocks being the first to be eniplaccd, 
and consequentl\' coming in contact with the meta- 
morphic rocks on all sides. The original sizes and 
shapes of most masses were destroyed by later gra- 
nitic intrusives, ^^•hich tore them apart and recr\stal- 
lized, granitized, and assimilated their fragments. Partl\ 
as a result of original differences, and partly because 
of subsequent modification, the mafic plutonic rocks 
are heterogeneous in composition and texture. Ver\' 
likely they include rocks of diverse origin, some hav- 
ing been mafic volcanic or calcareous sedimentar\ 
rocks. Alan\- bodies of dark granodiorite and some 
bodies of quartz diorite may be hybrids of more silicic 
granitic rocks and diorite, hornblende gabbro, or am- 
phibolite. The fabric of these suspected hybrid rocks 
is generally highh- irregular; some rocks are very 
coarse grained and in places contain poikilitic horn- 
blende crystals an inch or more long. 

Larger Features of the Granitic Rocks 

The more leucocratic granitic rocks, which make 
up the bulk of the batholith, are in discrete masses 
or plutons, \\hich are in sharp contact with one an- 
other or are separated bv thin septa of metamorphic 
or mafic igneous rock. Individual plutons vary greatl\ 
in size; their outcrop area ranges from less than a 
square mile to more than 500 sq mi. The limits of 
many of the large plutons have not yet been deline- 
ated. On the whole the batholith appears to consist of 
a few large plutons and a great man\- smaller ones, 
which are grouped between the large plutons (fig. 1). 
All of the large plutons, and some of the smaller ones, 
are elongate in a north\\esterly direction, parallel with 
the long direction of the batholith, but many of the 
small plutons are elongate in other directions or are 
rounded or irregularly shaped. 

The major plutons in the western part of the batho- 
lith are generally older than those along the crest of 
the range, and in the Yosemite region Calkins (19.^0) 



has mapped two series of granitic formations in w hicii 
the plutons are successively Nounger toward the east. 
Nevertheless, the pattern of intrusion is more compli- 
cated than a simple west-to-east sequence of emplace- 
ment. 

Isotopic dates of plutons in the central Sierra Ne- 
veda indicate three widely separated epochs of plu- 
tonism at > 183 m.y. and probably no more than 210 
m.y. (Late Triassic or Earl\- Jurassic), 124-136 m.y. 
(Late Jurassic), and 80-90 m.y. (early Late Creta- 
ceous). In addition, one large plutonic formation in the 
western half of the batholith, granodiorite of "Dinke\ 
Creek" type (fig. 1), is at least 115 m.y. old, but ma_\' 
not be as old as Late Jurassic. The ages of man\ 
mapped plutons have not been established in terms of 
meaningful isotopic dates, and some plutons ma\' have 
been emplaced in epochs of magmatism that have not 
yet been recognized. Although it is possible that the 
isotopic dates are simply points along a period of con- 
tinuous magmatism, it is difficult to conceive of a 
parent magma continuing to e.xist for more than 100 
m.\-. It seems more likel\- that magma was generated 
at intervals within this time span. 

The isotopic dates, together with intrusive relations 
observed in the field, indicate that plutons of similar 
ages are distributed not haphazardl\' but in geographic 
belts. The plutons of Late Triassic or Early Jurassic 
age lie along the east side of the batholith, and they 
ma\' be closelx- related to isolated plutons of about the 
same age span farther east and southeast in the In\-o 
and Argus Mountains (Ross, 1965, p. 046-048; Hall 
and MacKevitt, 1962, p. 30-31). Plutons of known 
Late Jurassic age in the central Sierra Nevada are 
confined to the western metamorphic belt, and it is 
likel\' that some plutons in the west side of the batho- 
lith are also of that age. The Late Cretaceous plutons 
constitute a belt, which averages about 25 miles in 
width, e.xtending along and just west of the Sierran 




Photo 3. Intrusive breccia. A (left)— Fragn 
later quartz monzonite. 



ntation of metamorphic rock by gronit 




(right) — Fragmentation of early quartz diorite by 



118 



Geology of North ikn California 



Bull. 190 




Photo 4. Felsic dikes in horn- 
blende gobbro. Parent to dikes is 
quortz monzonite in foreground. 



crest. This belt is interrupted south of Yosemite b\- 
a cross septum of metamorphic and pre-Late Creta- 
ceous plutonic rocks, which provides a window into 
an earlier period in the development of the batholitli. 

Bateman and others (1963, p. D38) have listed ten 
relations, which taken together indicate that the ma- 
jor part of the granitic rocks crystallized from melts. 
These include such relations as sharp contacts of plu- 
tons with wall rocks and with one another, dikes and 
inclusions along contacts between plutons from which 
the relative ages of the plutons can be determined witli 
consistent results, finer grain size in apophyses and in 
the margins of some plutons, wail-rock geometr\- that 
suggests dislocation by the emplacement of plutons. 
and dilated walls of aschistic dikes. The plutons are 
pictured as having moved upward from a deeper 
source region, much like .salt domes, because molten 
granitic magma has a significantly lower specific gra\ - 
ity than rock of the same composition. As the plu- 
tons rose, the country rock is believed to have settled 
downward around the magma, thus providing room 
for its continued upward migration. Conceivably, 
some plutons may have become entirely detached from 
their source region and be underlain by country rock, 
but no field evidence for downward bottoming of 
plutons has been found. 

The relative importance of several processes in the 
emplacement of the plutons has been onl\- incom- 
pletely evaluated. Wall-rock deformation indicates that 
rising magma squeezed the wall and roof rocks aside 
and upward. Sloping appears to have been important 



locally, but there is little evidence in support of stoping 
as the principal mechanism of emplacement. Processes 
of granitization and assimilation have operated on a 
small scale where the \\ all and roof rocks were amphi- 
bolites or other mafic rock, but these processes are of 
possible quantitative importance only in terranes of 
mafic volcanic rocks. Melting and assimilation of pe- 
litic rocks has not been proved, but ver\ likely has 
taken place and may have been of considerable im- 
portance. 

Broad chemical and mineralogic changes take place 
across the batholith. In general, the granitic rocks are 




Photo 5. An exceptional abundance of K-feldspor phenocrysts 
the marginal part of a pluton of proph/ritic quartz monzonite. 



1966 



Bateman and Wahrhaftk;: Sierra Nevada 



119 



7 



more mafic toward the west and more silicic toward 
the east, but this is a gross trend, and some silicic plu- 
tons occur in the western half of the range and some 
mafic plutons are within the eastern half. The simple 
explanation that the more felsic rocks in the east half 
of the range are differentiates of the more mafic rocks 
in the west half does not hold for several reasons: (1) 
Lengthy time gaps probably exist between the differ- 
ent age groups. (2) Large granodiorite and quartz 
diorite plutons in the west half of the range are ac- 
companied by younger and more felsic plutons, which 
are older than the large granodiorite and quartz mon- 
zonite plutons in the east side of the range. ( 3 ) The 
limited analytic data now available indicate systematic- 
ally lower K^O/NaoO ratios in the Jurassic granitic 
rocks of the western part of the range than in either 
the Cretaceous or the Early Jurassic or Late Triassic 
rocks farther east. 

Textures of, the Granitic Roclcs 

The granitic rocks of the central Sierra Nevada 
have been grouped into formations and less formal 
units on the basis of similarity of composition, texture, 
and intrusive relations or other evidence of relative 
age (Bateman and others, 1963, p. D13). Each of the 
granitic rocks is characterized by a "typical appear- 
ance," which is determined largely by grain size, con- 
tent of dark minerals, and texture. Except for un- 
common local variants the granitic rocks are medium 
grained; hypidiomorphic-granular; equigranular, seri- 
ate, or porphyritic; and contain 2 to 20 percent of dark 
minerals. 

The average grain size of most nonporphyritic rocks, 
and of the groundmass of the commoner porphyritic 
ones, is from 1 to 5 mm. Phenocrysts range widely in 
size; some K-feldspar phenocrysts are several inches 
long. Grain size is partly dependent on the size and 
shape of the pluton; the average grain size of large 
plutons is generally greater than that of smaller ones 
of the same composition. Equigranular rocks are com- 




Pboto 6. Flattened mafic inclusions In granodiorite. 



moner than porphyritic or seriate ones, but rocks with 
all three textures are well represented. 

The porphyritic rocks can be placed in two groups, 
those with phenocrysts of K-feldspar and those with 
phenocrysts of other minerals but none of K-feldspar. 
The phenocrysts of larger plutons generally are 
K-feldspar, whereas those in finer grained dikes, mar- 
ginal rocks, and apophyses are generally minerals that 
crystallized early, such as hornblende or plagioclase. 
Phenocrysts of K-feldspar are largely restricted to 
rocks of intermediate to calcic quartz monzonite or 
potassic granodiorite composition. They cannot be ex- 
plained in the same way as phenocrysts of most other 
minerals, which are formed early, because their many 
inclusions of other minerals show that they formed 
during the later rather than the earlier stages of crys- 
tallization. Nevertheless, dimensional orientation of 
K-feldspar phenocrysts near external contacts and in 
dikes shows that they were formed before the com- 
plete consolidation of the granitic rock. The presence 
of K-feldspar porphyroblasts in certain wall rocks and 
inclusions, which appear to be exactly like K-feldspar 
phenocrysts in contiguous granitic rock indicates 
pressure-temperature conditions like those in the 
magma, but does not indicate that the phenocrysts in 
granitic rock are porphyroblasts. 



Many granitic rocks of mafic quartz monzonite, 
granodiorite, or quartz diorite composition contain 
mafic inclusions, which have greatest dimensions of 
a few inches to a few feet. In any given area the in- 
clusions are generally all of about the same size and 
shape, but both size and shape vary from pluton to 
pluton and even from place to place within the same 
pluton. Commonly the mafic inclusions appear elon- 
gate in outcrop and are disc-shaped in three dimen- 
sions, but in some places they are subrounded or 
irregular in shape. ProbabK- many are triaxial, but the 
difference between the two axes that lie in the plane 
of flattening generally is too small to determine. Spin- 
dles have been reported, but in most places they have 
resulted from postconsolidation cataclastic deforma- 
tion (photo 6). 

In many plutons mafic inclusions are progressively 
flatter toward the margins of the pluton — a relation- 
ship that suggests the inclusions were soft when they 
were suspended in the granitic magma and were shaped 
by movements of the magma. To obtain disclike shapes 
probably requires stretching in all directions parallel 
to the disc, and could occur in the marginal part of a 
pluton during emplacement as a result of growth 
brought about by the continuing introduction of 
magma into the central part of the pluton. Triaxial 
mafic inclusions could result from unequal stretching 
in the plane of flattening. 

Mafic inclusions are present in quantity only in the 
granitic rocks that contain hornblende, although not 
all hornblende-bearing granitic rocks contain mafic 



120 



Gfoi.ocy of Northkrn California 



Bull. 190 




^,^- 



4V; 



■■■/I 



Iff- 




#■" 





Photo 7. Joints m gromtic rocks. A (above)-Deep slot eroded olong joif 
orthogonal joints in mud ium groined aloskite. 



^ 



grained quartz monzonite. B (opposite)— Closely spaced 



1966 



BaTF.MAN and VVaHRIIAFTIC; SiF.RRA NrVADA 



121 




inclusions. Where the composition of a piuton changes 
and becomes more feisic, both hornblende and mafic 
inclusions may disappear. For example, many concen- 
tricially zoned plutons contain abundant hornblende 
and strongly flattened mafic inclusions near their mar- 
gins but are free of both hornblende and mafic inclu- 
sions in their interiors. This relationship suggests 
strongly that mafic inclusions were stable only in 
magmas in which hornblende also was stable. 

Primary Foliation and lineotion 

Many of the granitic rocks are conspicuously foli- 
ated, and in others foliation can be determined by 
careful observation, but some feisic quartz monzo- 
nites and alaskites have no megascopically discernible 
foliation. Foliation is shown by flattened mafic inclu- 
sions and by the preferred orientation of tabular and 
prismatic minerals. Where both flattened inclusions 
and minerals with preferred orientation are present in 
the same piuton, they define foliations that are grossly 
parallel. Ho\\ever, the foliation defined by the pre- 
ferred orientation of minerals may show minor irregu- 
larities that are not reflected in the foliation defined 
by the mafic inclusions. The preferred orientation of 
minerals doubtless results from the same movements 
of the enclosing magma that shaped the mafic inclu- 
sions, but because the minerals are smaller than the 
inclusions they were more sensitive to minor or local 
movements within the magma. Linear structure is best 
shown by preferred orientation of elongate minerals, 
especially hornblende, but in a few places is shown 
by a systematically longer direction within the plane 
of flattening of the mafic inclusions. 

Compositional Zoning Within Plutons 

Some granitic plutons are obviously composition- 
ally zoned, and others not obviouslv zoned are found 



on careful study to show systematic variation in com- 
position from place to place. Compositional zoning 
is shown by variations in the amount of all of the 
major constituents, but is most readily evident in the 
field from variation in the content of mafic minerals. 
The simplest and best method of determining zoning 
in the laboratory is to measure the specific gravities 
of systematicalK' collected hand specimens. Zoning 
is generally either concentric or lateral. Concentrically 
zoned plutons generalK- are more feisic in the cores 
and more mafic toward the margins. Laterally zoned 
plutons are more feisic toward one side or one end — 
more commonly toward one end. Some very large 
plutons exhibit patchy or streak\' zoning. Some com- 
positional zoning can be related to contamination by 
wall rocks, but much zoning, particularly concentric 
zoning, is independent of the composition of the wall 
rocks and probably represents difi^erentiation processes 
within the magma. Much work remains to be done in 
defining the mineralogical and chemical changes that 
take place in plutons, in relating these changes to field 
observations of wall rocks and inclusions, and in in- 
terpreting these with the aid of pertinent experimen- 
tal studies of melts of granitic composition. 

Regional Joints 

.\ regional s\stem of conjugate joints is conspicu- 
ous in the eastern Sierra Nevada but indistinct in the 
western part of the range. These joints dip steeply 
and are not to be confused with the gently dipping 
sheeting that is subparallel with topographic surfaces 
and doubtless related to the physiographic develop- 
ment of the landscape; nor are they to be confused 
with cooling joints, which can be identified only 
where occupied by dikes and dike swarms. In the 
eastern part of the range joints are strongly reflected 



122 



Geology of Northfrn California 



Bull. 190 



in the topography in man\' places. On the floors of 
glaciated vailcxs and basins, and in regions of low- 
relief, such as the Tungsten and .\iabama Hills at the 
base of the eastern escarpment, linear depressions fol- 
low joints; even in deepi\- dissected regions straight 
segments of streams comnionl\' are joint controlled. 
Detailed examination of a few areas in the western 
part of the range reveals that joints also are common 
there but are indistinct and not reflected in the topog- 
raphy. Why joints are more conspicuous in the east- 
ern than in the \\ estern part of the range has not been 
satisfactorily explained. One possibility is that the de- 
velopment of sheeting ma\- tend to suppress the open- 
ing of steep joints. For example, the magnificent domes 
of the Yosemite regions owe their forms to exfoliation 
sheeting and to the fact that steep joints have not 
opened. Domes are notably lacking east of the Sierran 
crest where joints are conspicuous. Another possibility 
is that the steep eastern escarpment provides a free 
face that permits joints to open toward it. 

The joints are regional and are not confined to spe- 
cific plutons — thev cross boundaries between plutons, 
commonly with little or no deflection. General!)' it is 
possible to identify two principal sets almost at right 
angles, one set striking northeast and the other north- 
west. The direction of strike changes somewhat from 
place to place; where this occurs, the strike of both 
sets generally changes so as to maintain the right-angle 
relationship. 

Commonly the joints in a given set are nearly paral- 
lel, but in some places nearly parallel joints cross one 
another. Most joints are straight or genth' curved, and 
where a significant change takes place in the strike of 
a joint set, the joints of one strike generalh' interfinger 
with the joints of another strike. Some individual joints 
can be traced for several miles. The spacing between 
the joints ranges from less than an inch to hundreds 
or even thousands of feet. Regional differences in spac- 
ing exist, but within a given region the spacing of the 
joints appears to be primarily a function of the average 
grain size of the rocks — the widest spacing is in the 
coarsest rocks. Thus the spacing of joints developed 
under constant stress conditions is roughly propor- 
tional to the number of mineral entities between joints. 
The most conspicuous joints are widely spaced, be- 
cause where the joints are closel>' spaced the rock 
breaks into rubble, and systems of linear depressions 
do not form. 

The facts that the joint pattern is regional and that 
the joint sets are continuous across boundaries between 
plutons indicates that the joints formed after consoli- 
dation of the entire batholith. The joints are also pre- 
Eocene in age, because the thick zone of weathering 
in the granitic rocks beneath the F.ocene auriferous 
gravels extends downward into the unweathered rock 
along the joints. Furthermore, dikes of andesite, feeders 
to the Miocene and Pliocene Mehrten Formation, are 
intruded along the jf)ints. 



SPECULATIONS ON THE ORIGIN OF THE BATHOLITH 

The localization of the batholith in the axial region 
of a synclinorium of great size and depth compels 
serious consideration of the hypothesis that the granitic 
magmas were generated by the melting of sialic rocks 
of the upper crust as a result of their being depressed 
into deeper regions of high temperature. Experimental 
studies show that at atmospheric pressure sialic rocks 
begin to melt fractionally at 960°C, but that an in- 
crease in water-vapor pressure causes the melting tem- 
perature to drop spectacularly (Turtle and Bowen, 
1958). At pressures above 1 kilobar and in the presence 
of enough water to saturate any amount of magma 
that ma\' be generated, melting begins at temperatures 
between 600° and 700"C, the temperature var\ing in- 
versely with the pressure. If certain other substances, 
such as fluorine or chlorine, are present, the tempera- 
ture at which melting begins is lowered further. 

The first melt is composed chiefly of normative 
quartz, orthoclase, and albite, in proportions that are 
diff^erent at different pressures of water vapor; this 
melt probably is saturated or nearly saturated with 
water. To form more calcic magma more of the 
source rock must be melted, which requires higher 
temperatures. To form magma of quartz diorite com- 
position requires a temperature increase of about 
200°C above the temperature of the beginning of melt- 
ing if the melt is water saturated, and more if under- 
saturated. Because the amount of water soluble in 
magma may be quite high (about 10 percent by weight 
at 5 kilobars) and because the source rock is unlikel\- 
to contain more than a few percent of water at most, 
magmas of quartz monzonite, granodiorite, and quartz 
diorite are probably undersaturated with water. These 
considerations indicate that a temperature of 1,000°C 
or more is required to produce a granitic magma with 
normative plagioclase of Anju composition. 

The depth at which sialic rocks can be expected to 
melt to granitic magma is difficult to evaluate because 
our present knowledge of the generation and distribu- 
tion of heat in the earth is still in a primitive state. In 
stable parts of the crust where all the heat is carried 
to the surface b>' conduction, temperatures of 600° 
to yoO^C may be attained at depths of }0 to 50 km, 
but a temperature of 1,000^C ma\- not be reached at 
depths twice as great. However, the situation in a 
dow nfolding synclinorium is not ordinar\- because the 
crustal rock is greatly thickened in the downfold. 
Sialic rocks generall>' produce more heat than basaltic 
rocks, and the heat production in a dow nfolded sialic 
la\er thickened two or three times may be of sufficient 
magnitude to cause melting to occur in the low er part 
of the downfold (A. H. Lachenbruch, oral communi- 
cation, 1965). Measurements of the heat being pro- 
duced in the exposed framework rocks by radioactiv- 
ity would make possible some limiting calculations, but 
have not yet been made. Another possible source for 
heat is by upward movement of hotter material from 



1966 



Bateman and Wahrhaftig: Sierra Nevada 



123 



deeper levels either by intrusion or by convection 
within the mantle. Convection currents in the mantle 
have been postulated by Vening Aleinesz (1934), 
Griggs (1939), and nian\' others in connection with 
the formation of deep geosynclinal troughs. 

The model that emerges from these considerations is 
a magma zone that begins at a depth of 30 to 50 km 
and extends downward to the lowest level of depressed 
sial. At the top of the zone of melting, the ratio of 
hydrous felsic magma to solid rock is probably ver\' 
small. If no migration of material occurs within the 
zone of melting, the ratio of magma to rock increases 
downward, and the melt is progressively less hydrous 
and richer in calcium, iron, and magnesium. Very 
likely, however, this model would be modified by dif- 
fusion of water from the hydrous upper part down- 
ward into the less hydrous Io\\er part, and possibly 
also by convective circulation in the more completely 
fluid lower part, which would cause homogenization 
of the magma. 

In terms of a developing synclinorium, the first 
magma would form when the lowest sialic rocks were 
depressed into the zone of melting. Further depression 
of these same rocks would cause additional melting to 
form a magma richer in calcium, iron, and magnesium, 
and poorer in water. At the same time, new magma 
would form at the top of the melting zone in higher 
rocks. Because the density of granitic magma is signifi- 
cantly less than granitic rock of the same composition, 
the magma would tend to w ork upward in the manner 
of a salt intrusion, e.xploiting lines of structural weak- 
ness w^herever possible. Some magma would perhaps 
break through to the surface in volcanic eruptions, but 
much of it \\ould cr\-stallize at depth as plutons — 
which is what happened. Closely related sequences of 
granitic rocks that are successively more felsic with 
age and concentrically zoned plutons that are progres- 
sively more felsic toward the center indicate magmatic 
differentiation during emplacement from parent 
magma of granodiorite or quartz diorite composition. 
However, some compositional differences in geneti- 
cally related sequences, especially among the volcanic 
rocks, may reflect differences in parent magmas 
formed at different depths in the zone of melting. 

In the Sierra Nevada, the rocks that were melted 
doubtless included upper Precambrian, Paleozoic, and 
Mesozoic strata, but a major source of material prob- 
ably was the underlying Precambrian. In the Death 
\^alley region the Precambrian terrane is composed 
of quartzose and micaceous schist, amphibolite, and 
granitic gneiss. In addition to these sialic rocks, femic 
material from the lower crust and perhaps also the 
mantle must have been incorporated in the parent 
granitic magmas to supply the required calcium, iron, 
and magnesium, although upper Precambrian and Pale- 
ozoic carbonate formations like those exposed in the 
White and Inyo Mountains and in roof pendants of 
the eastern Sierra Nevada doubtless supplied some cal- 



cium and magnesium. Ultramafic and mafic intrusions 
in the western metamorphic belt, and basalt flows and 
hypabyssal intrusives, indicate that mafic material was 
introduced into the upper crust, and some of this 
mafic material must have been depressed with the 
enclosing rocks into the zone of melting; mixing of 
sialic and femic material could also have occurred at 
the base of the sial, in the zone of melting. Hurley 
and others (1963, p. 172) have determined the initial 
Sr^'/Sr'"' ratio of the granitic rocks of the central Sierra 
Nevada to have been in the range of 0.7073 ± 0.0010; 
thev deduced from this ratio that if the granitic mag- 
mas originated from a mixture of sialic and basaltic 
materials the ratio was one-third basalt and two-thirds 
sial. 

The fact that the plutonic rocks in the east side of 
the range are both younger and more felsic than those 
in the west side seems compatible \\ith differentiation 
processes within a single parent magma. However, 
Moore (1959, p. 206) has inferred from systematic 
difference in K-O/Na-O ratios that the rocks on the 
r\vo sides of his quartz diorite line, which runs through 
the Sierra Nevada parallel with the long axis of the 
range, are derived from different parent magmas and 
are not differentiates of a single parent magma. This 
interpretation is supported by isotopic dates that sug- 
gest gaps of man\- millions of years between the time 
of emplacement of some of the largest plutons on the 
two sides of the range (Kistler and others, 1965). Fur- 
thermore, the Mesozoic volcanic rocks also are more 
felsic toward the east even though some, and perhaps 
most, of the eastern volcanic rocks are older than the 
western ones. 

Moore (1959, p. 206) suggested that his quartz di- 
orite line "is probably parallel to and not far distant 
from the edge of the granitic (sialic) layer in the con- 
tinental crust," and that "granitic rocks emplaced east 
of the line are generated within a thick sialic layer, 
whereas those emplaced west of the line are developed 
within the sima or a thinner sialic la\er with great 
thickness of associated geosynclinal sediments and vol- 
canic rocks." Westward thinning of the sialic layer 
is in accord with interpretations of Bailey and others 
(1964, p. 7, p. 143, fig. 35 on p. 164) that the Fran- 
ciscan Formation was deposited on an oceanic rather 
than a continental crust. 

A reasonable interpretation of the compositional, 
geographic, and temporal relations of the granitic 
rocks is that magma w as generated several times, each 
time in a somewhat different area as a result of shift 
in the locus of downfolding (fig. 2). The isotopic 
ages indicate three epochs of magmatism but do not 
preclude other epochs. The oldest epoch is represented 
by granitic rocks that lie along the east side of the 
Sierra Nevada and have isotopic ages of 200 ± 20 m.y. 
(Late Triassic or Early Jurassic). They are chiefly 
quartz monzonite and granodiorite and are not as 
mafic as the next younger granitic rocks of the west- 
ern foothills, v\ hich are chiefly granodiorite and quartz 



124 



Gkoixxvy ok Nokthkkn California 



Bull. 190 



LATE PALEOZOIC 

T 




PRESENT DAY 






20 30 40 so Ml 



10 20 X W 50 60 70 80 Kn 



1966 



Batf.man AM) W'ahrhaki 



SiFRRA NkVADA 



125 



dinrite and have isotopic ages of 130 ± 10 ni.y. (Late 
Jurassic). The youngest plutonic rocks are those along 
the crest of the range, w hich have isotopic ages of 80 
to 90 m.y. (early Late Cretaceous), and are more 
felsic than the rocks to the west. These young rocks 
also ma\' be more felsic than the Late Triassic or Earl\' 
Jurassic rocks to the east, but before meaningful com- 
parison can be made of these two groups more an- 
alytic data than are now available will be required, 
and the age assignments of plutons will have to be 
made more precise. 

The picture envisaged is that the sialic upper crust 
was downfolded and thickened, possibly as the result 
of convective overturn in the earth's mantle, so that 
the lower part of the downfold was at or near the 
melting temperature of sialic rocks. Periodic deforma- 
tion then caused further downfolding that produced 
magma in one part or another of the downfold, and 
the magma rose to form plutons and volcanic rocks. 

If this hypothesis is correct, tectonic episodes should 
have immediately preceded and accompanied epochs 
of plutonism and volcanism. At the present time the 
data are permissive only, and the hypothesis cannot be 
tested until the times of plutonism and of tectonism 
have been more closel\' delineated. The only estab- 
lished temporal relation between tectonism and plu- 
tonism is that of the well-known Late Jurassic Ne- 
vadan orogeny to Late Jurassic plutonism. One of the 
older periods of deformation that have been recog- 
nized in the metamorphic rocks could well be tem- 
porally related to the Late Triassic or Earl\- Jurassic 
plutonism, and deformation in the western metamor- 
phic belt that occurred after the Nevadan orogeny 
could be an expression of tectonism at the time of the 
early Late Cretaceous plutonism, but these suggested 
relations have not been established. 

Northwest and west of the Sierra Nevada, in the 
Klamath IMountains and northern Coast Ranges, Irwin 
(1964) has recognized two periods of deformation. 
One of these he identifies as the Late Jurassic Ne- 
vadan orogeny, and the other as a Late Cretaceous 
orogeny, w hich he designates as the Coast Range or- 
ogeny because of its "importance in development of 
the pre-Tertiary structure of the Coast Ranges." East 
of the Sierra Nevada, in western and southern Nevada, 
several periods of compressive deformation since Late 
.Mississippian time are generally recognized, and some 
of them appear to have occurred at about the same 
time as the plutonic episodes of the Sierra Nevada. 

Temporal correlations between plutonic and vol- 
canic rocks may be possible at some future time, but 
at present all that can be said is that the volcanic rocks 
span most and perhaps all of the known epochs of 
plutonism. \'olcanic rocks of Early Jurassic age have 



Figure 2 (opposite). Cross sections illustrating a model for mogn 
generation and emplacement in the Sierra Nevada. The sections a 
drawn in accordonce with the discussion in the text. 



been identified in the eastern Sierra Nevada, and ones 
of Late Jurassic age have been identified in the west- 
ern metamorphic belt, but most volcanic sequences are 
unfossiliferous, and their precise ages are unknown. 

•According to Eaton and Healy ( 1963) the crust be- 
neath the high central Sierra Nevada is at least 50 
kilometers thick, about twice as thick as the crust 
west of the range and 15 to 20 kilometers thicker than 
the crust beneath the Basin and Range province east 
of the range. Not only is this geophysical root cen- 
tered beneath the highest peaks, at least in the central 
Sierra Nevada, but it also lies beneath the belt of 
Cretaceous plutons. These coincidences suggest that 
the root was formed b\- dow nfolding of the crust at 
the time of the early Late Cretaceous magmatism, and 
that uplift of the Sierra Nevada during the Late Creta- 
ceous and Cenozoic was caused by a mass deficiency 
of the root. Negative isostatic anomalies (Oliver, 1960) 
and analysis of first-order leveling of the U.S. Coast 
and Geodetic Survey by Oliver (written communica- 
tion, 1965) that indicates the central Sierran crest has 
risen during a 60-\ear period at the rate of about a 
centimeter per year support the concept of a net mass 
deficiency extending from the surface downward to 
some depth of compensation. A serious difficulty with 
this hypothesis is that an expectable consequence is 
continuous uplift, though at a steadily diminishing rate, 
until the root has disappeared. The geologic record in- 
dicates, however, that little or no uplift took place 
during an e.xtended period of 25 to 30 million years 
that included much of Eocene and Oligocene time. 
Nevertheless, the Sierra Nevada has certainh' been up- 
lifted and deeply eroded, and a better explanation for 
the uplift than mass deficiency has not been devised. 

DEPTH OF EROSION SINCE MESOZOIC PLUTONISM 

In 1963 Bateman and others published a speculation 
that 1 1 miles (about 17 km) of rock has been stripped 
off the Sierra Nevada since the batholith was em- 
placed. To arrive at this speculation the\- inferred that 
the water-vapor pressure (Pn^ii) '" the most highly 
fractionated magmas and in the thermally metamor- 
phosed wall rocks was about 5 kilobars, and assumed 
that Ph2(> = Pioad (pressure equivalent to the weight 
of the overhing rocks). Since then, Putman and Alfors 
(1965) have inferred that the Pn.o during crystalliza- 
tion of the Late Jurassic Rocky Hill stock in the 
western foothills was about 1.5 kilobars, and S\Ivester 
and Nelson (1965) have inferred that the Pi,.,, during 
crystallization of the Cretaceous Birch Creek pluton 
in the White Mountains was 2 to 3 kilobars. In both 
reports Pn^o was considered to equal Piood- 

Since Bateman and others' speculations were pub- 
lished much additional information has become avail- 
able, some of which casts serious doubt on the validit\' 
of the assumption that Pn.o = Pio„d. In view of this 
doubt, arguments that require making the assumption 
that Phjo = PioHd are excluded from the following 
discussion. 



126 



Gf.ology of North frn California 



Bull. 190 




Figure 3. Map of the western United States showing the general distribution of land and sea duri 
the Late Cretaceous. Isopochs show thickness of Cretaceous sediments in the Rocky Mountain geosynclii 
Modified from two illustrations by Gilluly (1963). 



Unfortunately, there is no simple way to measure 
the amount of rock that has been stripped away, and 
the problem can be attacked only indirectly. In the 
following discussion, two approaches are pursued: 
One is an evaluation of the volume of sediment of 
latest Jurassic, Cretaceous, and Cenozoic age that had 
its source in the Sierra Nevada, and the other is con- 
sideration of the significance in terms of load pres- 
sure of andalusite and sillimanite in thermalK' meta- 
morphosed wall and roof rocks. 

During the Cretaceous, the Sierra Nevada w as part 
of a north-trending highland that lay between the 
Rocky Mountain geosyncline on the east and the 
Pacific coastal region on the west (fig. }). .\ccording 
to Gilluly (196.^ p. 146-147), 

"The Rocky Mountain geosyncline eventuolly come to hold more 
than o million cubic miles of dominontly clastic sediment, about 
five-sixths of it of Cenomonian (early Lote Cretaceous) ond younger 
age (Reeside, 1944; Gilluly, 1949). Only o relatively smoll port 
of this volume was of juvenile volcanic rocks; the overwhelming 
bulk was derived from erosion of older rocks. The ostensible source 
area, that is, a lorge port of the orea between the Rocky Mountain 
geosyncline ond the Pacific geosyncline, was only about 160,000 
squore miles— ot the most generous estimate 200,000 square 
miles. If this were indeed the whole source, on overage denuda- 
tion of about 5 miles is implied. The bulk involved is tremendous; 
it is equal to that which would be furnished by slicing 1,600 feet 
from the entire area of the United States. While this volume was 
accumulating in the eastern port of the cordilleron region, clastic 
beds of comparable or perhaps even greater thickness were ac- 
cumulating in the Pacific geosyncline, west of the Sierra Nevada." 



The Cretaceous and Tertiar\ deposits along the 
Pacific Coast are chiefly epiclastic and in a large part 
were deposited in a geosynclinal environment. Un- 
fortunately-, discontinuity of exposures and strong 
deformation prevent calculating their volume from 
isopachs as Gilluh- was able to do for the miogeosyn- 
clinal strata of the Rock\- .Mountain gcos\ncline. If 
seems safe to assume, however, that at least as much 
sediment collected in the Pacific coastal region as in 
the Rocky Mountain geos\ncline. 

A few volume estimates of local areas can be cited, 
but for most parts of the Pacific coastal region the 
data arc inadequate for calculations of sediment vol- 
ume. The Franciscan Formation of latest Jurassic and 
Cretaceous age is one of the thickest and most exten- 
sive formations. Baile\- and others (1964, p. 21) state. 

"By for the most abundant rock of the Franciscan is groywocke, 
which hos a truly astonishing volume. Even if the overoge thickness 
is regarded as only 25,000 feet |they estimate the thickness to 
be 50,000 feet], ond the depositionol area in California ond off 
shore is about 75,000 square miles, the total volume of the Fran- 
ciscan groywocke is more than 350,000 cubic miles." 

In considering the .source of the Franciscan. Bailc\ 
and others (1964, p. 146) state, 

"The source of the older, pre-Knoxville Fronciscon seems most 
likely to be the ancestral Klomoth Mountoins ond Sierro Nevada 
lying east of the depositionol area. The source of some of the 
debris forming the younger Franciscan rocks probably olso lay in 



1966 



Batfman AM) Wahrhaktic: Sifrra Nevada 



127 



the same area, but it seems unlikely that this would have been the 
source of all the younger Franciscan rocks." 

They offer two suggestions for the source of certain 
younger rocks which, are essentially free of K-feldspar, 
an unknown western source, and cannibahsm of up- 
lifted older Franciscan rocks. 

Calculations from isopach maps prepared by Repen- 
ning (1960) indicate that the volume of shelf and 
slope facies Cretaceous and Tertiary strata beneath 
the Great Valley is about 100,000 cubic miles. No 
estimates are available for the Cretaceous and Tertiary 
strata of the Coast Ranges exclusive of the Franciscan, 
but their volume may approach the volume of strata 
beneath the Great Valley. Thicknesses and volumes 
of Cretaceous and Tertiary marine strata in western 
Washington and Oregon are not as well known as in 
California, but are probably comparable. Thus the 
volume of sediment of latest Jurassic to Recent age 
in California is at least 550,000 cubic miles, and a 
volume of a million cubic miles for the entire Pacific 
coastal region of the United States does not seem out 
of line. 

The total area of the highland that lav between the 
Rocky Mountain geosyncline and the Pacific coastal 
region within the boundaries of the United States was 
about 400,000 square miles. If the volume of latest 
Jurassic to Recent rocks along the Pacific Coast of the 
United States is taken to be equal to volume of sedi- 
ments that accumulated in the Rocky Mountain geo- 
syncline, and the total is figuratively redistributed over 
the intervening highland, they would bury it to an 
average depth of 5 miles. To convert volume of sedi- 
ment to depth of rock eroded requires an adjustment 
for differences in the density, but need for this adjust- 
ment is more than offset bv loss of almost all the ver\- 
considerable volume of carbonate that was present in 
the source area, but present in small amounts in the 
depositional basins (Gillul\', 1963, p. 147). Doubtless 
much suspended and fine clastic material also was lost. 

Undoubtedly some parts of the source area have 
been more deeply eroded than others. In the Sierra 
Nevada, isostatic adjustment following deep down- 
folding probabl\' caused greater uplift and conse- 
quently deeper erosion than took place in central and 
eastern Nevada. If erosion of onl\- the Sierra Nevada 
is considered, it seems reasonable to look at the epi- 
clastic sedimentary rocks that lie directly to the west. 
The possibility of long shore drift of sediments and 
of movement along the San Andreas and other faults 
introduces very considerable uncertainty into the cal- 
culation, but the probability that the volume of sedi- 
ment has been increased by faulting is less than that 
it has been reduced, for the San Andreas cuts off the 
Franciscan Formation on the southwest. 

Most of the sediments that underlie the Great Val- 
ley undoubtedly were eroded from the Sierra Nevada, 
either directly or by the reworking of older deposits 
that were derived from the Sierra Nevada. If to the 



volume of sedimentary rocks beneath the Great Val- 
le\' are added half the geosynclinal deposits of the 
Coast Ranges and half the Franciscan Formation, a 
conservative total of 325,000 cubic miles of sedimen- 
tary rocks are attributed to erosion of the Sierra Ne- 
vada. The Sierra Nevada is 400 miles long and averages 
about 80 miles wide if the downslopc continuation of 
the range beneath the east side of the Great Valley is 
included, giving an area of about 32,000 square miles. 
Thus the volume of sediment attributed to erosion of 
the Sierra Nevada is sufficient to bury the range to a 
depth of more than 10 miles. This figure can be com- 
pared with an estimate by Little (1960, p. 99) that 
35,000 feet of rock was eroded from the Nelson batho- 
lith of British Columbia during the Portlandian Stage 
of the Upper Jurassic and the entire Cretaceous; Little 
suggests that an equal amount was eroded during 
the Cenozoic. 

The other approach to the problem of the amount 
of stripping is through consideration of the pressures 
during the thermal metamorphism of the wall and roof 
rocks implied by recent studies of the ALSiO.-, poly- 
morphs contained in these rocks. In 1963, Bell reported 
the results of experimental studies of the stability of 
andalusite, sillimanite, and k\anite; and in the same year 
Khitarov and others published the results of studies 
of the same minerals and mullite plus quartz. The data 
contained in these two reports are in good agreement, 
and Waldbaum (1965) has prepared a composite plot 
from the tabulated data of Bell and Khitarov and 
others (fig. 4). The pressure and temperature at the 
triple point for andalusite, sillimanite, and k\anite are 
believed to be quite reliable, but the pressure and tem- 
perature at the triple point for andalusite, sillimanite, 
and mullite plus quartz are less \\ell established. 

In the Sierra Nevada, andalusite is a common alumi- 
nosilicate in the contact metamorphosed wall and roof 
rocks (Durrell, 1940, p. 44-45; Hietanen, 1951, p. 
575; Rose, 1957, p. 642; Bateman, 1965, p. 24; Moore, 
1963, p. 9-13), but in many places, especially adjacent 
to intrusive rocks, andalusite gives way to sillimanite 
(Knopf, 1917, p. 233-234; Durrell, 1940, p. 46-47; 





0< 

5 


TEMPERATURE 
> 200 400 600 


c 

aoo 1 


s 


' 1 1 1 > 1 1 


- 


II 


10 

1 5 


Andiluslta 1 


Mu 1 1 1 1 e ind 
qua r t z 


I 


20 




\^ : 


^ 


25 




\. 


t- 

z 
o 


30 
35 


^^-s:^ Sill 
Kyaniti \^ 

1 , 1 1 i\ 1 


iman ite 



Figure 4. Fields of stability of andotuslte and its polymorphs 
according to Watdboum (1965). (Modified slightly.) 



X 



128 



Gkoi.ogy of Northfrn California 



Bull. 190 



Rose, 1957, p. 642). These relations show that where 
andalusite occurs the pressure during metamorphisiii 
must not have exceeded the upper limit of its stabilitx , 
which is about H.6 kilobars according to the experi- 
mental data, and that \\ here sillimanite also occurs the 
pressure must not have fallen below the lowest pres- 
sure limit of its stability, which is about 4 kilobars. 
The absence of k\anite suggests that the pressure was 
less than 8.6 kilobars — prol)ably less than 7.5 kilobars. 

The pressures involved in the formation of andalu- 
site and sillimanite are total pressures and are not de- 
pendent on the presence or absence of water because 
the two minerals are pol\morphs. Tectonic overpres- 
sures during metamorphism are unlikel\- because the 
metamorphisni that produced both minerals was caused 
by magma, w hich should have relieved an\- significant 
overpressure by upward movement. If the pressures 
reflect the weight of the overlying rocks, as seems to 
be required, and if an average dcnsit\' of 2.8 is assumed, 
the limiting pressures of 4 and 7.6 kilobars correspond 
to limiting depths of 15 and 27 km (9 and 17 miles, 
respectively).' 

Thus both lines of evidence followed here suggest 
erosion from the Sierra Nevada of the same order of 
magnitude as was suggested, perhaps fortuitousl)-, by 
Bateman and others in 1963. The time span of this 
amount of erosion is the time since the Nevadan 
orogeny and intrusion of the Late Jurassic granitic 
rocks. The exposed early Late Cretaceous granitic 
rocks must have consolidated under less cover than 
the exposed Late Jurassic granitic rocks, and it mav 
not be accidental that all occurrences of sillimanite 
thus far reported, with the possible exception of the 
sillimanite reported b\- Ro.se (1957), are along con- 
tacts with the older granitic rocks. 

THE SUPERJACENT SERIES 

On the deeply eroded metamorphic and granitic 
rocks of the Sierra Nevada rests a nearly fiat lying 
sequence of sedimentary and volcanic rocks of Late 
Cretaceous and Cenozoic age, which Lindgren, Turner, 
and Ransome in their geologic folios called the Super- 
jacent series. Where these rocks are found, they were 
deposited after the great depth of erosion described 
in the preceding paragraphs was completed. The earl\- 
geologists believed that the unconformit\- at the base 
of these rocks represented a hiatus in the recorded 
histor\- of the Sierra Nevada, but it now appears that 
Cretaceous sedimentary rocks were being deposited 
along the western margin of the range when the gra- 
nitic rocks we now see along the crest of the range 
were being intruded. 

' In early 1966, after this paper was in galley proof, D. F. Weill 
(Geochim. et Cosmochim. Acta, v. 30, no. 2, p. 223-238) and 
R. C. Newton (Science, v. 151, no. 3715, p. 1222-1225) published 
data that sugfiest the ptcssuic at the andalusitekyanite-sillimanite 
triple point is significantly less than is indicated bv the data of Bell 
(1963) and Khitarov and others (1963). According to Newton, 
andalusite cannot be stable at a pressure greater than 4.2 kilobars, 
corresponding to a depth of 15 km (9 miles). Until the divergent 
experimental data have been reconciled, the pressure indicated by 
the coexistence of andalusite and sillimanite in the same terranc must 
rem.iin in doubt. 



The Superjacent series is most extensive, and the 
histor\ it records most complete, in the northern Sierra 
Nevada north of the Tuolumne River. The most com- 
plete sequence is along the western foothills, w hek^e 
there arc a few exposures of sandstone, conglomerate, 
and shale of the Late Cretaceous Chico Formation, a 
few exposures of early Eocene sandstone and shale, 
and much more extensive exposures of the middle 
Eocene lone Formation, which consists of quartz- 
anauxite sandstone, kaolin-rich claystonc, and coal, 
deposited during a brief period of almost tropical 
climate. The equivalent deposits within the range arc 
the prevolcanic auriferous gravels. These indicate that 
erosion dow n to the present level of exposure of the 
granitic rocks was complete throughout the northern 
Sierra Nevada b\' middle Eocene time. Overlying the 
sedimentar\' formations are two sequences of volcanic 
rocks: ( 1 ) rh\()litic eruptives of Oligocene to middle 
.Miocene age, and (2) andesitic mudflows, lavas, and 
conglomerate of late Miocene to late Pliocene age. 

These formations bury a topograph)- with as much 
as .3,000 feet of local relief, indicating that the Sierra 
Nevada was not reduced to a peneplain at the end of 
the great denudation. Many unconformities occur 
within the Superjacent series, but the general accord- 
ance of stream gradients of Eocene to Pliocene age 
indicates that during much of the Tertiary the Sierra 
Nevada was essentiall\- stable. The Superjacent series 
also indicates that, beginning in the Pliocene, the 
Sierra Nevada was tilted westward and broken b\- a 
complex system of faults along its eastern margin. 
Uplift along the crest amounted to 4,000-7,000 feet. 

1 he southern part of the range lacks an extensive 
superjacent cover like that found in the northern 
Sierra Nevada, but scattered remnants of basaltic flows 
and a few sedimentar\' deposits along the western 
margin record essentially the same story. 

The history of the Sierra Nevada in Late Cretaceous 

and Cenozoic time depends on the interpretation of 
exposures at a few critical localities, for the super- 
jacent deposits are now fragmentary. The sections that 
follow contain frequent references to these localities, 
which arc shown on figs. 5 and 6. 

Upper Cretaceous Rocks (Chico Formation) 

Upper Cretaceous marine scdimentar>- rocks of the 
Chico Formation crop out along the west base of the 
Sierra Nevada in four main areas. In the extreme north. 
Cretaceous rocks are exposed resting unconformabl\' 
on metamorphic rocks in the can\ons of Big Chico 
Creek and other streams draining the south end of the 
Cascade Range just west of the Sierra. The thickest 
section, about 2,800 feet on Big Chico Creek, is the 
type localit)- for the Chico Formation, and consists of 
about 500 feet of conglomerate at the base, grading 
upward to arkosic wacke. It ranges in age from Coni.i- 
cian to middle Canipanian (Matsumoto, ;// Rogers, 
1962). 



1966 



Batf.man and VVahrhaitk;: Sierra Niaada 



129 



The Chico is also exposed at Pentz, about 8 miles 
northwest of Oroville. About 5 miles cast of the Pentz 
locaiit\% the lowermost gravels of the Cherokee Hy- 
draulic mine at the north end of Oroville Table Moun- 
tain consist largely of boulders and cobbles of green- 
stone from adjacent bedrock. The upper part of this 
"greenstone gravel" is a zone of rotted boulders and 
intercalated red cla\', apparently a zone of deep 
weathering. Topical quartz-pebble auriferous gravel 
overlies this weathered zone. Allen (1929) and Creele\' 
( 1955) suggest that the "greenstone gravel" may cor- 
relate with the Chico in the Pentz area. 

Two exposures of fossiliferous sandstone and shale 
of the Chico Formation have been reported by Lind- 
gren (1894; 1911, p. 22) from the vicinity of Folsom. 
Here a few feet of sedimentar\- rocks, with a little 
gold-bearing gravel at their base, rest in depressions in 
the bedrock surface cut on granodiorite (K-Ar age, 
136 m.y., R. W. Kistler, oral communication, 1965) 
and the Eocene lone Formation and Pleistocene auri- 
ferous gravels overlie them. 

About 400 feet of arkosic sandstone containing Cre- 
taceous fossils was intersected in a boring about 5 miles 
south of Friant on the San Joaquin River (Macdonald, 
1941, p. 259). Granitic rocks crop out 1 '/i miles to the 
northwest in the south end of Little Table ^Mountain 
at altitudes higher than the wellhead, indicating con- 
siderable relief on the pre-Cretaceous surface. About 
8 miles northwest of the well and about 2 miles west 
of California Highway 41, a roadcut along the Friant- 
Madera Road contains an outcrop that ma\' be the 
feather edge of the Cretaceous beneath the Eocene 
lone Formation. In this roadcut, white and light-brow n 
anauxitic sandstone typical of the lone Formation rests 
on deeply weathered gabbro and metamorphic rocks. 
The weathered zone is characterized by thorough de- 
composition of the original minerals and by mottling 
in brilliant purple, red, and white — all colors character- 
istic of the tropical weathering profile at the base of 
the lone Formation elsewhere. At the east end of this 
outcrop, the weathering profile is developed on 
dense structureless fine-grained material that contains 
rounded pebbles of quartz, chert, slate, and decom- 
posed granitic and metamorphic rocks. This material 
is here interpreted as thoroughly decomposed pebbly 
arkosic beach or stream sand, of possible Late Cre- 
taceous age, weathered before the lone Formation was 
deposited. 

The Cretaceous exposures described above indicate 
that the bedrock surface along the western margin of 
the Sierra Nevada was eroded to its present depth by 
Maestrichtian time at the latest, approximately 65 to 
70 m.y. ago, and in part by Coniacian time, 85 to 90 
m.y. ago. 

Although biotite dates on the granitic rocks of the 
western Sierra Nevada range between 124 and 136 
m.y., these dates have probabh' been reduced as a 
result of reheating by later intrusions, and this belt of 



granitic rocks was probably emplaced during the 
Portlandian stage of the Jurassic, 140 to 145 m.y. ago. 
Consequently between 9 and 17 miles of cover was 
eroded from the western Sierra Nevada in a time in- 
ter\al of between 55 and 80 m.>., or at a rate of '/i 
to 1 '/: feet per thousand \ears — a rate comparable 
w ith the highest rates of denudation measured today. 

Lower Eocene Deposits of the Foothills 

Allen (1929, p. 368-369) described a sequence of 
gray shale and biotite-rich .sandstone along the banks 
of Dry Creek and near the west base of Table Moun- 
tain, 8 miles north of Oroville, which is about 80 feet 
thick and contains casts of Corbiculci. These beds dip 
about 4° SW. and are overlain, apparently unconform- 
ably, by the lone Formation. They are distinguished 
from the lone by an abundance of detrital biotite, 
hornblende, and feldspar, minerals that are lacking in 
the lone and believed to indicate that the climate dur- 
ing early Eocene time probably was not as tropical as 
during lone time. Similar material from a shaft about 
2 miles north of Oroville contained an early Eocene 
fauna equivalent to that of the Meganos Formation 
(Allen, 1929, p. 369). 

Gray clay exposed at clay pits near Lincoln, which 
Allen (1929, p. 363) called the Walkup Clays, may 
correlate with the beds at Dry Creek. No exposures of 
these pre-Ione beds have been found farther south, 
but they have been penetrated in borings beneath the 
lone Formation. In Jackson X'alley, between lone and 
\'alley Springs, as much as 65 feet of sandstone similar 
to that on Dry Creek was encountered in boring into 
valleys as much as 400 feet deep that are buried by 
the lone Formation (Pask and Turner, 1952). Farther 
west, between Lodi and Oakdale, several hundred feet 
of dark-gray biotite-bearing feldspathic sandstone and 
shale, with marine or brackish fossils of Eocene age, 
were encountered in deep wells (Piper and others, 
1939, p. 85-86). 

lone Formation 

The lone Formation is exposed discontinuously 
along the west base of the Sierra Nevada from Oro- 
ville Table Mountain southward to Friant (Allen, 
1929). Nearly everywhere it rests on a deeply weath- 
ered surface with a local relief of as much as 1,000 
feet cut in crystalline basement (Allen, 1929; Pask 
and Turner, 1952). 

Pask and Turner (1952) have shown that the lone 
Formation consists of two members, separated by an 
erosional unconformity with as much as 130 feet of 
relief. The lower member is chiefl\' ( 1 ) sandstone 
consisting predominantly of quartz and large flakes 
of the clay mineral anauxite (kaolinite with excess 
silica) and with little or no feldspar, biotite, horn- 
blende, or other heavy minerals; (2) clay beds con- 
sisting largely of kaolinite or halloysite; and (3) a icy 
lignitic coal beds, ranging from a few inches to 24 
feet in thickness. The upper member consists of sand- 
stone with abundant feldspar and common biotite and 



130 



Geology of North frn California 



Bull. 190 




EXPLANATION 



Chann* It ot PI ioein* t. 

(X/eried where position 

uncertain 



Mioctni and youngar rocks 
of tha Qraat Vallay 



ChanntU of Eocana to 

Hiocana a|a 

Dast)ed wt)ere approximate 

queried where uncertain 



lona Foraat Ion 



Probabia or igina I aitant 

of aur ifarout grava la In 

Tart lary Yuba latin 



Figure 5. Mop thowing locolitiei in northern Sierra Nevada mentioned in text, and prevolcanlc and intarvolcanic channels, lone Forniatian, and 
inferred original distribution of auriferous gravels in the basin of the Tertiary Yuba River. Channels from: Gold Belt Folios; lindgren, 1911, plate 1; 
Browne, 1890; Storms, 1894; Clark ond others, 1963; Goldman, 1964. lone Formation from Chico sheet, Sacramento sheet (prelim, comp.), and San 
Jose sheet (prelim, comp.) of Geologic Map of California, Olaf P. Jenkins edition. 



1966 



Bateman and Wamrmauk;; Surra Nevada 



131 




Figure 6. Map showing localities in southern Sierro Nevada mentioned in text, and locations of Cenozoic 
volcanic rocks in southern Sierra Nevada dated by the potassium-argon method (from Dalrymple, 1963; 1964o, b- 
Doell, Dalrymple, and Cox, 1966). 



132 



Gkoi.ckjy ok Nokthikn Cai.ikorma 



Bull. 190 




Photo 8^ Exposure of auriferous gravels in the Malokoff Diggings, North Bloomfield, Nevoda County, California. Photograph by Mary Hill. 



chlorite, interbedded \\ith kaolinitic cla\- of slightly 
different composition. The presence of larger amounts 
of unstable minerals in the upper member than in the 
lower suggests that either the climate had grown sig- 
nificantly less tropical or accelerated erosion had 
brought fresher material from the base of the weather- 
ing profile to the surface. The lone Formation gen- 
erally rests on a lateritic weathering profile. Commonl\ 
only the white lithomargic cla\- of the lower part of 
the profile is preserved, grading into the underlying 
weathered bedrock. Localh' the iron-rich crust of a 
typical laterite is preserved, and transported laterite, 
some containing as much as 44 percent iron, is inter- 
bedded in basal beds of the lone on the flanks of buried 
highlands. 

The lone Formation shows marked lateral variation 
in lithology, and interfingering of beds of sand and 
clay. It is general!)' thought to have been deposited 
under deltaic and lagoonal conditions, with coal 
swamps accumulating in quiet waters behind an outer 
ridge of islands; channel crossbcdding and gravel lenses 
in much of the coarser part suggest deposition by 
fluviatile processes. The presence of thin la\'crs with 
remains and casts of marine shells in the sands indicates 
periodic incursions by the sea. 



The maximum thickness reliably reported is about 
450 feet (Piper, Gale, and others, 19.^9, p. 84), al- 
though Turner (1894) reported a thickness of about 
1,000 feet. Pask and Turner estimated a maximum 
thickness of 415 feet for their lower lone and between 
163 and 225 feet for their upper lone, but the total 
thickness at any one place is considerabl\- less than 
the sum of these figures because the upper member 
overlaps the lower across an erosional unconformity. 

A marine mollusk fauna reported by Dickerson 
(1916) has been placed in the middle Eocene Capay 
Stage by Mcrriam and Turner (1937). On plate 16 in 
Bowen (1962), the lone Formation is shown as later- 
ally continuous with Kreyenhagen Shale of late Eocene 
age. 

The mineral assemblage of the lower lone and the 
thick lateritic soil on which it rests indicate a tropical 
climate with perhaps alternations of wet and dry sea- 
sons for the period of \\eathering that led to the 
formation of its sediments (.A.llen, 1929). The irregular 
buried topography beneath the formation, and the 
erosional unconformity within the formation, suggest 
gradual relative rise in sea level and alluvial ponding 
of the lower valleys, interrupted by at least one period 
of relative lowering of base level during the accumu- 
lation of the lone. 



1966 



Batf.man AM) VV'aiirhaI' tic;: Sikrra Nk.vada 



133 




Canozoie vclcmie roeki 



Auriferous |r**(ls 



Area probably ca«ared by 
pravoleenic fraveli at 
their ireatett eiteet 



Channels ol Eeeaiie Tafea 
River and its t r ibetar ies 

2000 

Contours on surface buried by 
prevolcanic gravels, and 
its subeerial eitensien 
Contour interval 500 feet 



Modern Yuba River end 
major tributeries 



Figure 7. Mop of Nevada City quadrangle, showing auriferous grovel d 
extent of gravels, and topography on surfoce buried by the Cenozoic roclcs. 
Folio; and original reconnaissance survey. For location of quadrangle see figi 



Prevolci 



els 



The high-level gold-bearing gravels of the northern 
Sierra Nevada make possible a rather detailed recon- 
struction of the early Tertiary topography of the 
range, as well as an estimate of the amount and char- 
acter of the late Cenozoic deformation of the range. 
Magnificent e.xposures of these gravels, produced 
through hydraulic mining from 1855 to 1890, have 
been eroded to fantastic badlands; many segments of 
the original bedrock channels have been laid bare on 
the floors of the hydraulic pits. 

Most of the auriferous gravels were deposited before 
the major period of volcanic activity in the Sierra 
Nevada. These earlier gravels will be called the pre- 



;posits, channels of Tertiary Yuba River, probable original 
Data from Whitney, 1880; lindgren, 1911, and Smortsville 
ire 5. 

volcanic gravels in the pages that follow. iMany other 
gold-bearing gravels, however, \\ ere deposited in chan- 
nels cut during the period of volcanic eruptions or in 
la\'ers intercalated with the volcanic deposits. In ac- 
cordance with the usage of Lindgren (1911), these 
gravels will be called the intervolcanic gravels.* 

The prevolcanic gravels are found as irregular or 
sinuous patches on the relatively' flat interfluves be- 
tween the deep canyons of the northern Sierra Nevada. 
Some of the gravel patches clearly define the sinuous 

' Some volcanic eruptions, notably those recorded by the Wheatland For- 
mation and Reeds Creek Andesite of Clark and Anderson (1938) and 
some of the eruptions in the extreme northern part of the Sierra (see 
Durrell, this bulletin) may have taken place before deposition of 
some of the Tprevolcanic gravels described in this article. 



134 



Geology of Northern California 



Bull. 190 



channels of the large rivers that drained the earl>' 
Tertiary Sierra Nevada — for example, the channel 
gravels between French Corral and Nf)rth San Juan 
(fig. 7). Other gravel patches cap broad areas of 
ancient valleyside benches, or are found on present- 
day hilltops, unrelated to any identifiable channel. 
Many of the gravels crop out discontinuousl>' along 
the ha.sal contact of the Tertiar\- volcanic rocks, and 
have been explored beneath the volcanics b\' extensive 
drifts of gold mines. 

From a study of the altitude and disposition of the 
various bodies of prevolcanic gravels, VVhitne_\' (1880) 
and l.indgren (1911) were able to discern on the west 
slope of the Sierra Nevada a former svstem of five 
major rivers with tributary branches and several minor 
streams. The major streams were named by Lindgren 
the Tertiar\' Yuba, American, Alokelumne, Calaveras, 
and Tuolumne Rivers, after the modern streams 
which reach the Great \'alley at the approximate 
points where the provolcanic rivers reached the sea. As 
can be seen in figure 5, the Tertiary Yuba and Cala- 
veras were the major streams which drained the Gold 
Belt, in contrast to the relatively- small streams now- 
bearing those names. The south forks of both of these 
Tertiary streams flowed for several miles through the 
foothills in northwestward trending valleNS, following 
a belt of soft slate l\-ing east of ridges of massive 
greenstone. These northwestward trending courses are 
critical in evaluating the late Cenozoic tilting of the 
range. 

The piecing together of the courses of the prevol- 
canic rivers w as the work of many years. Earlv geolo- 
gists, and most miners, believed that the auriferous 
gravels were deposited by a series of north-trending 
streams that flowed approximately perpendicular to 
the present drainage (cf. Trask, 1854). The great con- 
tribution of the Whitney Survey to the stud>- of the 
auriferous gravels was the demonstration that the 
gravels were deposited by streams that flowed west 
and southwest (Whitney, 1880). Lindgren (1911) 
solved the remaining problem by showing that the 
northwest-trending belt of gravels between Forest 
Hill and North Columbia marks the prevolcanic 
South Fork of the Yuba River. The anomalous slopes 
of the prevolcanic channel in this belt he explained as 
the result of subsequent tilting of the range. Chandra 
(1961 ) has questioned Lindgren's interpretation of this 
belt, but imbrication of pebbles and crossbedding in a 
critical part of the channel, exposed along Highw ay 40 
at Gold Run (Hudson, 19.'>5), confirm that the stream 
that deposited these gravels flowed north. 

The thickness of the prevolcanic gravels is variable, 
partly because of the irregular topography on which 
the\- were deposited and partly because of erosion 
cutting into them before the deposition of the volcanic 
formations. The greatest thickness of gravel is in the 
deposits of the Tertiary Yuba River, and reaches 500 
to 600 feet in the diggings between North Columbia 



and Gold Run. In contrast to the thick gravels de- 
posited along the Tertiarv Yuba River, the prevolcanic 
gravels deposited along the other rivers are onl\- lo- 
cally- more than 50 feet thick. 

The prevolcanic gravels consist doniinantly of 
pebble and cobble gravel with interbedded sand and 
cla\-. 1 he average size of pebbles in the gravel is be- 
tween '/2 and 1 Vx inches, and the maximum size in an\ 
gravel layer, except near the base of the graxels, is 
rarel\- more than 9 inches. Near the base of the gravels, 
however, the boulders are much larger, with some re- 
ported to be 5 to 20 feet across. Most of these boulders 
are of adjacent bedrock and may have been brought 
to the channel by tributary torrents or tumbled into 
it from undercut' banks. Even large boulders well 
above the base of the section could have been incorpo- 
rated in the gravels in this fashion, and the size of 
these rare giant boulders is not necessarilv a measure 
of the competence of the Tertiary streams. 

In terms of pebble population the prevolcanic grav- 
els are of two contrasting t\-pes, although intergrada- 
tions exist. One t\-pe, known to the miners as "blue 
gravel," consists of a wide variet\- of pebbles, repre- 
senting most of the bedrock in the drainage basins of 
the streams. In this type of gravel, where exposed at 
Smartsville or North San Juan, for example, the pre- 
dominant rock tvpes are meta-andesite, schi.st, and 
slate; quartz and chert make up 20 to .30 percent at 
most. Granitic pebbles are rare but persistent com- 
ponents. These "blue gravels" commonlx- fill the bot- 
toms of the main channels. The other type, known 
as "white gravel," generall\- overlies the "blue gravel' 
in the main channels and rests on bedrock benches. 
It is made up largel\- of quartz, chert, and quartzite, 
which usuall\- constitute 60 to 70 percent of the peb- 
bles, with quartz being the most abundant. The re- 
mainder of the pebbles are opaque w hite pebbles, now- 
consisting largely of clay that can be crushed between 
the fingers. These mav originalK- have been metamor- 
phic or igneous pebbles, weathered to white cla\- fol- 
iowing deposition. 

Practically all the pebbles except those of quartz 
and chert are weathered. .Most nonsiliceous pebbles 
can be cut with a fingernail or knife, although in man\ 
exposures of the "blue gravels," resistant metavolcanic 
and granitic pebbles are common. The pebbles could 
not have been transported in this weathered condition, 
so presumably most w ere weathered after deposition. 

The sands interbedded with the gravels var\- in com- 
position with the gravels. Studies by Galen Sturgeon 
(/';/ .MacGinitic. 1941 ) of a cross section of the gravels 
exposed at ^'ou Bet show that the sands associated 
with the basal blue gravels arc arkosic and contain 
biotite, hornblende, and epidote among the heavy min- 
erals, whereas sands associated with the white quartz- 
rich gravels consist almost entirely of quartz and 
anauxite or of quartz with bleached biotite. These 
latter sands accumulated under climatic conditions 



1966 



Bateman and Wahrhaftig: Sierra Nevada 



135 




EXPLANATION 






Figure 8. Sketch from photograph of roadcut 1 mile west of North Columbia, Nevada County, California, showing local 
unconformities probably caused by lateral migration of an oggroding stream into bodies of overbank silt on its floodplain. 
Vertical exaggeration 2 X . 



comparable to those of the lone Formation, and are 
probably to be correlated with the lower member of 
the lone (Pask and Turner, 1952). At the top of the 
auriferous gravels at You Bet are about 150 feet of 
crossbedded biotite-bearing sand with abundant fresh 
feldspar, clearly representing conditions of less ex- 
treme weathering than the sand below. This upper 
sand may correlate with the upper lone of Pask and 
Turner (1952) or with the Wheatland Formation of 
Clark and Anderson (1938). 

In the thick gravel sections of the Tertiary Yuba 
River the average pebble size decreases toward the 
upper part of the section, and the proportion of cla\' 
and sand increases. Discontinuous layers of plastic clav 
are common throughout the upper part of the pre- 
volcanic gravels, but are rare in the deep channel 
gravels. In man>- of the drift mines, the top of 
the section contains 2 or 3 beds 10 to 50 feet thick 
of dense white "pipe-cla\"' (cf. Lindgren, 1911, pi. 
25). Most of these are apparently floodplain deposits, 
but some may have been deposited in tributary chan- 
nels dammed by aggradation along the main channels. 
Contacts of some of the clay beds with the overlying 
sand and gravel are local unconformities marked by 
channels, and angular blocks of clay, apparently torn 
from the clav beds, are found in the overlying gravels 
(fig. 8). 

The upward decrease in grain size suggests that the 
river was growing less competent, possibly because of 
a relative rise in base level or a decrease in overall 
gradient. The significance of this for the tectonic his- 
tory of the Sierra Nevada is discussed in a subsequent 
section. 

According to Lindgren (1911, p. 71) fine gold is 
distributed throughout the entire thickness of the 
gravels, generally to the value of 2 to 10 cents per 
cubic yard in the upper gravels, but the bulk of the 
gold and all the coarse pieces were concentrated within 
3 feet of bedrock, where the gravel in the mines ran 
from 50 cents to $15 per cubic yard (at a price of 
$21.00 per ounce of gold). Commonly the richest de- 
posits, those justifying drift mining, were in a narrow 



streak at bedrock along the deepest part of the chan- 
nel, and the maps of the old drift mines serv'e therefore 
to delineate the thalwegs of the ancient rivers. Some 
of the gold was mined from the upper few feet of 
weathered bedrock, where it had been forced by the 
currents or had sunk during weathering. 

Allen ( 1929) showed that the lone Formation was 
deposited by the same streams that were depositing 
the auriferous gravels, and he found the lithology of 
the lone to be the same as that in the white quartz 
gravels, indicating that the prevolcanic gravels are of 
Eocene age. Paleontologic evidence from the gravels 
themselves confirms this. The prevolcanic gravels have 
yielded an extensive fossil flora, which was origi- 
nally described by Lesquereux (1878) and Knowl- 
ton (/'w Lindgren, 1911). The collections studied by 
Lesquereux and Knowlton were unfortunately mixed 
with collections from the intervolcanic gravels, and 
their age assignments are consequently in error. More 
recently collections from rhyolite tuff immediately 
overlying the auriferous gravels at La Porte have been 
studied b\' Potbury (1937) and collections from clay 
beds interbedded with the white gravels at Chalk Bluff 
and the You Bet diggings have been studied by Mac- 
Ginitie (1941). According to MacGinitie (oral com- 
munication, 1965), the Chalk Bluffs flora is late early 
Eocene; the La Porte flora is now regarded as early 
Oligocene (Wolfe, and others, 1961). A potassium- 
argon age of 32.4 m.y. has been obtained on the La 
Porte Tuff (Evernden and James, 1964). 

Thus the fossil and stratigraphic evidence indicate 
that deposition of the prevolcanic gravels took place 
during much of the Eocene and may have extended 
into the earliest Oligocene. According to MacGinitie 
(1941, p. 78), the climate during this time was char- 
acterized by an average annual temperature of 65 °F, 
slight seasonal variation in temperature with little or 
no frost, and an annual rainfall of 60 inches or more 
with maximum precipitation in the warm season — in 
other words, a subtropical climate similar to that along 
the coast of southern Mexico. 



n<. 



Gl-.OLCXiV OK N'OKTlltRN (ImiIOKMA 



Bull. 190 




Photo 9. 
the distono 
of the Cos. 



West-sloping interfluves and dendritic drainage of northern Sierra Nevoda, consequent upon the surface of the ondesltic mudflov 
on right can be seen the foothill belt of northwest-trending ridges of Jurassic greenstone. View looking south from over the headv> 
mnes River with the canyon of the Mokelumne River in the middle distance. U.S. Geological Survey photograph GS-OAH-6-68. 



Vole 



For 



and Intervolc 



of the Northern Sierra Nevodo 

Inasmuch as the Cenozoic volcanic formations of the 
northern Sierra Nevada are treated in papers by Dur- 
rell and Slemnions in this bulletin, only those aspects 
of these formations pertinent to the Cenozoic land- 
scapes and subsequent uplift will be treated here. 

The rhyolite tuffs, ash flows, and associated clastic 
rocks of the \'allev Springs Formation ( Piper and 
others, 1939), 20 to 30 million years old (Dalrsniple, 
1964), are in few places more than 800 feet thick 
(Slcmmons, this bulletin). They filled narrow valle>s 
in a landscape whose relief was more than 1,000 feet, 
and formed a continuous sheet only in the Great \'al- 
iey. They overtopped a few passes low on the west 
slope of the Sierra, notably those a few miles east of 
Nevada Cit>', to effect the first of a series of drainage 
changes (Lindgren, 1K96, 1911). The number of iden- 
tifiable eruptions during the 14-million-ycar period of 
rhyolitic eruptions is small. Contemporaneous streams 



had ample time to rew ork the volcanic deposits and to 
cut through the ash-flow plains to bedrock. The can- 
\ons cut through the rhyolitic deposits generally did 
not coincide with the prevolcanic channels, although 
they were as deep and in places deeper. 

The gravels associated with the \'alle\- Springs For- 
mation consist mostly of quartz and bedrock frag- 
ments; recognizable rhyolite pebbles are scarce ( Lind- 
gren, 1911; Browne, 1890; Goldman, 1964). ThcN- arc 
interbedded with rh\olitic tuffs or fill the bottoms of 
channels and are overlain by rh\olitic ash flows 
(called "white cement" b\- the miners). In part the\' 
result from erosion and deposition that took place just 
before or after the rh\olitic eruptions, and in part they 
result from later deposition in tributary valleys that 
were dammed by rhyolite flows. The scarcity of rhyo- 
lite pebbles is gencrall\- explained as due to the fragile 
character of the rhyolite tufi^. IMuch of the gold in 
these gravels ma\- have been reworked from prevol- 
canic gravels intersected by interrhyolitic channels. 



Batk.man and VV'ahrhaftig: Sierra Nevada 




Photo 10. Sinuous flat-topped mountain capped by a lotite flow filling an intervolcanic channel: Toble Mountain in Tuolumne 
County, capped by the Table Mountain Lotite Member of the Stanislaus Formotion, which flowed down the "Cataract Channel", 
a Pliocene course of the Stanislaus River. The Stanislaus now flows in the deep gorge extending from right to left across the 
photograph several miles beyond the mountain. The rolling uplands on either side of the mountain ore parts of the stripped 
unconformity at the base of the Superjacent Series. View northeost from between Jamestown and Melones, about three miles 
west of Sonoro. Rawhide Flat in lower left foreground. The town of Columbia in the distance on the extreme right. The 
northeast-trending light bands on the surface of the flow are unrelated to the course of the flow, and may be the surface 
expression of northeast-trending regional jointing, propagated upward from the basement into the Superjacent Series. Aerial 
photograph by John S. Shelton. 



iVIost of the auriferous gravels of the Tertiary Cala- 
veras River appear to be assignable to the interrhyolitic 
gravels (Lindgren, 1911; Storms, 1894; Goldman, 
1963). These gravels were rich in gold and locally are 
200 feet or more thick. 

Extensive andesitic mudflows and conglomerates 
were deposited during the interval following the de- 
position of the Valley Springs Formation, from 19 to 5 
million years ago (Dalrymple, 1964). They a\ ere con- 
siderably thicker than the Valley Springs, ranging 
from more than 3,000 feet thick along the crest of the 
Sierra to 500 feet in the foothills (Slemmons, this bul- 
letin), and they buried the bedrock topography of the 
northern Sierra Nevada almost completely. At the 
close of the andesitic period, the only bedrock high- 
lands rising above the andesitic plains were ridges of 
resistant greenstone along the western foothills, a few- 
high summits of the middle slopes, and a few ridges 
along the crest of the range, such as the mountains 
around Pyramid Peak. As a consequence of this burial, 
the prevolcanic drainage was entirel\- obliterated, and 
a new drainage consequent upon the depositional 
slopes of the andesitic deposits was developed. 



The andesitic deposits along the west foot of the 
range were named the iMehrten Formation by Piper 
and others (1939), and Curtis (1951; 1965) applied this 
name to the andesitic deposits at the crest of the range 
near Markleeville, which can be traced almost con- 
tinuously to the western foot of the range. Slemmons, 
in this bulletin, has split the andesitic deposits into 
three newl\- named formations, the Relief Peak (the 
oldest), Stanislaus, and Disaster Peak Formations. He 
feels that the Disaster Peak Formation probably cor- 
relates with iVIehrten of the t\pe locality. 

Only in a few places can more than 40 mudflows be 
identified in a single section of the andesitic deposits, 
so presumably the 14-million-\'ear period of andesitic 
eruptions \\as marked by long intervals without vol- 
canic activity \ during which the streams that coursed 
down the volcanic slopes had time to carve new can- 
\ons and valleys. These, in turn, would be filled with 
the products of new eruptions, and the Stanislaus For- 
mation, defined b\- Slemmons in this bulletin, occupies 
just such a valley. 

Some of the intervolcanic gravels of this period oc- 
cupy' the bottom of these channels and record stages 



138 



Gf.ology of Northern California 



Bull. 190 





SECT ION ALONG L I NE A 



W SECTION ALONG LINE B E 



WASH INGTON 

SHAFT r3500' 






mm mm 



SECTION ALONB LINE F 
EX P L ANA T I ON 

mm ^ 



Indetlllc Rhyollta |nt« r vo lean I c B I ot It • -bta r I ng clay 
■udflo« tuft grivelt tand 



Pravolcanic 
irava Is 



Bad r ock >or k Inia 



Figure 9. Cross sections of the chonnet of the Tertiary Yuba River along lines shown on figure 12. Sections A, B, and C from Ross E. Browne, 
1890; section D from MocGinitie, 1941. p. 19; sections along E and F constructed from 1:24,000 Smartsville and French Corral quadrangles with 
geology by Wahrhoftig. Vertical exaggeration 2 X. 



1966 



BaTEMAN and VVahRHAFTIG: SlFRRA Nf.vada 



139 



in the development of the present drainage. For exam- 
ple, the intervolcanic channel of the Forest Hill Divide 
represents the first period of diversion of the South 
Fork of the Tertiary Yuba River into the drainage of 
the American River. Similarly the "cataract channel" 
beneath the Table Mountain Latite Member of the 
Stanislaus Formation (see Slcmmons, this bulletin), 
records the establishment of the Stanislaus drainage 
basin at the expense of the South Fork of the Tertiary 
Calaveras River. 

The gravels associated with the andesitic eruptives 
contain abundant large cobbles of andesite, along with 
rarer clasts of bedrock and quartz. They only locally 
contain gold in paying quantities; the gold of the inter- 
volcanic channel of the Forest Hill Divide, which was 
mined over considerable distances, was probably re- 
worked from prevolcanic channels. 

The Tertiary Landscapes of the Northern Sierra Nevada 

Remnants of Tertiary landscapes of many different 
ages are preserved beneath the Tertiary gravels and 
volcanic deposits. Some notion of the character and 
minimum relief of the early Tertiary surface can be 
gained by drawing reconstructed contours on it, using 
remnants preserved beneath the Tertiary deposits and 
the surface of the existing pre-Tertiary bedrock in 
neighboring areas as control. Lindgren (1896) recon- 
structed the early Tertiary topography of an area 
around Grass Valley and Nevada City, on the upland 
between the present Yuba and Bear Rivers, and he 
showed this area to have had then almost as much 
relief as it does now. A similar reconstruction of the 
early Tertiary topography of the 15-minute Nevada 
City quadrangle is shown in figure 7, which includes 
the valley of the Tertiary Yuba River around North 
San Juan. Cross sections of the Tertiary Yuba and 
modern Yuba are shown in figure 9. From the cross 
sections, and b\' comparison of figure 7 to a topo- 
graphic map of the 15-minute Nevada City quadran- 
gle, it can be seen that local relief on the lower west 
slope of the Sierra Nevada amounted to as much as 
1,000 to 1,500 feet, which is about half of the total 
relief that exists there today. Other estimates of local 
relief include a few hundred to 1,800 feet in the lower 
part of the Tertiary Calaveras River, and as much as 
3,000 feet along the present crest of the Sierra, which 
is the amount that Pyramid Peak rises above the in- 
ferred level of the Tertiary American River (Lind- 
gren, 1911) and the amount that Mount Dana in Yo- 
semite Park rises above gravels at its west base which 
have been correlated with the auriferous gravels 
(R. W. Kistler, oral communication, 1965). These 
figures are all minimum figures, for they do not take 
into account erosion from the highlands during and 
after the deposition of the auriferous gravels. 

The general character of the Tertiary topograph\- 
was summarized by Lindgren (1911) who recognized 
three topographic belts: (1) in the western foothills 
close to the Great Valley a belt of greenstone ridges 



1,000 to 1,800 feet high but crossed b\' the Tertiary 
rivers in fairly narrow canyons; (2) a lowland eroded 
on the slates of the Mother Lode belt, in which were 
cut the valleys of the South Forks of the Tertiary 
Yuba and Calaveras Rivers; and (3) east of this low- 
land, a broad plateau, rising rather sharply to altitudes 
of 1,000 to 2,000 feet above the lowland, and incised 
to depths of a few hundred to a thousand feet by the 
valleys of the Tertiary streams. Isolated high moun- 
tains surmounted the plateau, notably along the pres- 
ent range crest. 

In detail the main valleys seem to have had a central 
gutter, a few hundred to a few thousand feet wide, 
underlain generally by fresh bedrock, and with steep 
and even overhanging fresh bedrock walls as much as 
40 feet high. This gutter, which is the main bedrock 
channel excavated for gold, was the bed or thalweg 
of the main stream, and is commonly filled with "blue 
gravel". On either side of the gutter the valley sides 
rose either as smooth slopes or as a series of benches, 
on which the quartz gravels rested generally on deeply 
weathered bedrock or a lateritic soil. The benches on 
the Yuba were '/z to 1 mile wide, and beyond them 
the land sloped more steeply to the uplands on either 
side. 

The location of the early Tertiary drainage divide 
is uncertain. Lindgren placed it at the present crest 
of the northern Sierra as far south as Lake Tahoe, and 
somewhat east of the crest south of Lake Tahoe. At 
least one piece of evidence makes it likely that the 
divide, in part, lay well to the east of the present crest. 
In the gravels at the base of the andesites around Eb- 
betts Pass and a few miles south of Sonora Pass are peb- 
bles of black chert unlike other chert in that part of the 
Sierra Nevada, and resembling most closely the Paleo- 
zoic chert exposed in western Nevada. Also in the 
Ebbets Pass gravels are pebbles of porphyritic quartz- 
monzonite that probabl)- came from the Topaz Lake 
quartz monzonite of Curtis (1951) cropping out east 
of the present divide. 

Cenozoic Volcanic Rocks of the Southern Sierra Nevada 

Few Cenozoic deposits are found in the Sierra Ne- 
vada south of the Tuolumne River, as erosion has 
probably been continuous in this southern area since 
the intrusion of the batholith. The few deposits that 
exist are chiefl\' of two kinds: volcanic rocks, which 
cover less than 1 percent of the surface, and glacial 
deposits. 

The volcanic rocks have an importance far beyond 
their areal extent, for they provide information on the 
time and amount of faulting, uplift, and canyon cut- 
ting b\- giving minimum ages for the surfaces and 
deposits on which they rest. They are chiefly basalt 
and andesite flows, but include basalt cinder cones, 
latite domes and volcanoes, and rhyolite tuffs and ash 
flows. Information on their age is largely from potas- 
sium-argon dates on sanidine or plagioclase of the 
siliceous rocks or on whole-rock basalt (Dalrymple, 



140 



Geology of Northern California 



Bull. 190 




Photo 11. View west over the heodwoters of the West Walker River a 
the superjacent series. Base of superjacent series is marked by dashed li 
at the north end of Yosemite Pork is in the distance on left, and Relief 
photograph. Light-colored rock in left half beyond the droinage divide 
slopes making up many peaks in right of the picture, including peak in the 

1963, 1964a, 1964b; Dalrymple, Co,\, and Doell, 196.>). 
The dated volcanic rocks fall into three groups in 
terms of age: 9 to 10 million years; 2 to 4 million 
years; and less than 1 million years. 

A date of 9.5 ±0.3 m.y. was obtained from basalt 
along the San Joaquin River about 20 miles northeast 
of Kriant (Dalrymple, 1963). This occurrence of Plio- 
cene basalt defines the local relief in the southern 
Sierra Nevada in Pliocene time, and also the amount 
of deformation since then (Dalrymple, 1963; Chris- 
tenscn, 1966; Wahrhaftig, 1965e). The dated basalt 
is from Sugarloaf Hill on the floor of Jose Basin, a 
broad bench about 1,700 feet above the San Joaquin 
River and surrounded by mountains 2,000 to 3,000 feet 
higher. Upstream along the San Joaquin River from 
Friant is a sinuous string of basalt-capped mesas and 
buttes, whose summits rise evenly eastward from river 



nd the drainage divide of the Sierra Nevada showing the southern limit of 
Ine. Valley of West Walker River is in the middle distonce. Dorothy Loke 
Peak in center. Sonoro Pass lies behind the peaks near the right edge of 
is mainly quortz-monzonite and gronodiorite; dark-colored rock with even 
foreground, is andesite. U.S. Geological Survey photograph GS-OAH-4-144. 

level at a point about 5 miles south of Friant to about 
2,500 feet about 15 miles northeast of Friant, forming 
a slope of 130 to 140 feet per mile. Beneath the basalt 
is as much as 320 feet of interbedded gravel and rhyo- 
lite tuff (iMacdonald, 1941). The basalt-capped moun- 
tains define an ancient channel of the San Joaquin 
River, which when projected eastward upstream coin- 
cides in altitude with the basalt of Sugarloaf Hill, and 
is therefore about 9.5 million years old. The level of 
this Pliocene stream is marked upstream by a series of 
benches along the canyon wall, and 10 miles north of 
Jose Basin, these benches, at an altitude of 4,000 feet, 
are bordered b\- mountains S.OOO to 10,000 feet high. 
Ihus during the Pliocene the southern Sierra Nevada 
had a local relief of 4,000 to 6,000 feet (Dalrymple, 
1963). 



1966 



Batkiman and Wahrhaki 



SllKRA Nl'.VADA 



141 



Basalt from Coyote Flat, about 10 miles southwest of 
Bishop, dated bv Dalrymple at 9.6 ± 0.2 m.y., occu- 
pies a shallov\' north-trending valley which was prob- 
ably established at the beginning of the warping of the 
Coyote Flat salient (Bateman, 1965). 

A number of undated basalt remnants are probably 
of early Pliocene or Miocene age, judging from their 
physiographic relations. A series of remnants along the 
canyon of the Kings River (Krauskopf, 1953) range 
in altitude from 3,000 feet at the mouth of the North 
Fork of the Kings River to about 5,500 feet near 
Hume Lake, 1 1 miles east, where they are 3,500 feet 
above the river. The slope of the channel defined by 
these basalt patches, if they are all remnants of the 
same flow, or are nearly contemporaneous flows, is 
about 140 feet per mile. Other flows that may have 
formed during this period are the fiow on Stony Flat, 
west of General Grant Grove (Burnett and Matthews, 
in press), and flows in the Bartolas Country at the 
forks of the Kern River (Miller and Webb, 1940; 
Smith, 1965). 

Dates in the range from 2 to 4 million years have 
been obtained for basalt flows in the Kern River Can- 
yon, on the upper San Joaquin River, and along the 
east side of the Sierra Nevada from the Alammoth 
Lakes area to the Owens Gorge. All these flows have 
been extensively eroded, and those on the east side of 
the range have been deformed. Few eruptive centers 
can be identified. 

At Trout Meadows, at the mouth of the Little Kern 
River, a basalt flow fills the inner gorge of the Little 
Kern to within a fe^\• hundred feet of the present 
stream level (Webb, 1953; Dalrymple, 1963). The ba- 
salt extends across the trace of the Kern Canyon fault 
without displacement. The date on the basalt of 3.5 
IT 0.1 m.y. shows that the bulk of the cutting of the 
upper Kern Canyon was completed by that time and 
that the Kern Canyon fault has been inactive for at 
least the last 3.5 million years. Evidence presented by 
Webb (1953) indicates that it has been inactive for 
a much longer period. 

Several flows in the upper San Joaquin basin have 
been dated at 3.3 to 3.5 m.y. (Dalrymple, 1963, 1964; 
Doell, Dalr\mple, and Cox, 1966). Most of these flows 
rest on the floor of the broad basin of the South Fork 
of the San Joaquin River or on mountain slopes graded 
to that basin. One flow, the basalt at Four Forks 
Creek, which is 3.5 m.y. old appears to have been dis- 
sected in the cutting of the inner gorge of the South 
Fork; on the other hand, flows dated at 3.5 and 3.3 
m.y. appear to have flowed as much as 500 feet down 
the walls of the inner gorges of the North and Middle 
Forks of the San Joaquin. Thus the cutting of the 
inner gorge of the San Joaquin seems to have started 
before about 3.5 million years ago. 

Part of the crest of the Sierra Nevada east of the 
headwaters of the Middle Fork of the San Joaquin is 
on basaltic andesite and latite, which fill a canyon cut 
to within 500 feet of river level — a canvon which 



drained westward across the present drainage divide 
(Hubcr and Rinehart, 1965b). The flows are cut off 
on the cast along the fault scarp that marks this part 
of the east face of the Sierra Nevada. A date of 3.0 
to 3.1 m.y. on these flows (Dalr>niple, 1964a) shows 
that prior to this time the San Joaquin River was re- 
ceiving drainage from at least part of the Mono Basin, 
and that much of the range-front faulting on the east 
side of the Sierra Nevada is less than 3 million rears 
old. 

At McGec Mountain, about 15 miles farther south- 
cast along the east front of the Sierra, basalt remnants 
on the mountain top were dated by Dalrymple (1963) 
at 2.6 ± 0.1 m.y. This basalt is overlain by the McGec 
till, which is believed by Putnam (1962) and Rinehart 
and Ross (1964) to predate several thousand feet of 
displacement along the eastern fault s\'stem of the 
Sierra Nevada. On the other hand, Lovejoy (1965) 
regards the basalt and till as post-faulting in age. 
Christensen (1966) discusses the evidence in this 
area, and concludes that the estimates of Putnam, and 
of Ross and Rinehart, are probably correct. 

Ten miles east of McGee Alountain, in Owens 
Gorge, basalt beneath the Sherwin Till has been dated 
at 3.2 m.y. (Dalrymple, 1963; for description of the 
locality, see Putnam, I960; Rinehart and Ross, 1957; 
and Wahrhaftig, 1965c). 

Undated basalt flows on the upland between the San 
Joaquin and Kings Rivers may belong to the 2- to 4- 
million-year period of volcanic eruptions. 

Quaternary volcanic rocks (those less than a million 
years old) are predominantly in three volcanic fields 
that are within or border the southern Sierra Nevada. 
One field includes Mono Lake, Alammoth Alountain, 
the Devils Postpile, and the Bishop Tuff. Another 
extends along the base of the Sierra Nevada between 
Big Pine and Independence. The third is around the 
headwaters of the South Fork of the Kern River. 

Dated volcanic rocks of the complex Alono Lake- 
Alammoth field range in age from less than a million 
\ears to about 6,000 years. The Bishop Tuff, dated at 
700,000 years (Dalrymple, Cox, and Doell, 1965) is a 
rhyolitic ash flow 400 to 450 feet thick that covers 
an area of approximately 350 square miles between 
Alono Lake and Bishop (Gilbert, 1938). It rests on till 
of the Sherwin Glaciation (Putnam, 1960a; Rinehart 
and Ross, 1957) and has been faulted and deformed 
with structural relief of possibly as much as 3,000 
feet. It is confined to the vallev between the Sierra 
Nevada and the White Mountains, and indicates that, 
although much of the range-front faulting took place 
after 700,000 years, the largest displacements took 
place before 700,000 years. Tuff identical to that of 
the Bishop Tuff also occurs in the valley of the Aliddle 
Fork of the San Joaquin River. Although geographic- 
ally separated from the Bishop Tufi^ by the present 
Sierra drainage divide, this tufi^ has tentatively been 
correlated with it (Huber and Rinehart, 1965a). The 
basaltic andesite of the Devils Postpile was subse- 



142 



Geology of Northfrn California 



Bull. 190 




Photo 12. Quoternory volcanic field at eost base of the Sierra Nevada south of Big Pine, with the east face and crest of the range in the bock- 
ground, as viewed west from Highway 395 about 6 miles south of Big Pine. Headwaters of Big Pine Creek is behind Fish Spring Hill on the right. 
Toboose Creek canyon on extreme left in background. Birch Mountain is the high white peak on skyline on right; Mount Tinemoha is the high 
mountain south of it. 

In the foreground is a basaltic cinder cone. The rough dark area in the plain at the right foreground is basaltic lava. The dork sharp-pointed hill 
below and left of Birch Mountain is a perlite dome. Photograph by Mary Hill. 



quently erupted into the Middle Fork valle>-, probably 
during an interglaciation. 

Mammoth Mountain is a large quartz-latite volcano 
on the crest of the Sierra Nevada near the head of 
the Middle Fork of the San Joaquin River. Dalr\mple 
(1964a) obtained an age of 370,000 years on a sample 
from the northwest part of the mountain; the moun- 
tain still shows signs of thermal activity (Huber and 
Rinehart, 1965a). 

From basaltic cinder cones several miles south of 
Mammoth Mountain a line of late Pleistocene and 
Recent eruptive centers extends northward through 
the Mono Craters to Black Point on the north shore 
of Mono Lake. Black Point is a basaltic cinder cone 
that apparcntl\' erupted during the last high stand of 
Mono Lake (Christensen and Gilbert, 1964). Cinder 
cones and basalt flows, erupted since Mono Lake 
dropped to its present level, make up parts of Negit 
and Paoha Islands in the lake. 

The Mono Craters are a series of rh\'olitic tuff rings 
and endogeneous domes, some of which have spread 
as stubby steep-sided flows as much as three-fourths 
of a mile from the vents, and which continue south- 
\sard from the main mass for several miles as a scries 
of plug domes. Potassium-argon dates of 6,000 years 
and 65,000 years have been obtained from the Mono 
Craters (Evernden, Kistler, and Curtis, 1959). At the 
southern end of this string of domes are two explosion 



pits, the Inyo Craters, which radiocarbon data sug- 
gest were formed between 500 and S50 years ago 
(Rinehart and Huber, 1965). 

At the south end of the line of eruptive centers lie 
the Red Cones, of Recent (postglacial) age, and Pumice 
Butte, of probable late Pleistocene Age (Huber and 
Rinehart, 1965a; 1965b). Pumice from eruptions along 
this line mantles a large area around the .Mono Craters 
and Mammoth Mountain and extends as far south as 
Kaiser Summit, east of Huntington Lake. 

Numerous basaltic cinder cones and flows lie along 
the base of the Sierran escarpment between Big Pine 
and Independence (Bateman, 1965; .Moore. 1963). 
Some flows are interbedded with outwash gravels that 
may be of Tahoe age, but others arc much older, being 
offset b\ faults with man\- tens or even hundreds of 
feet of displacement. A flow in Sawmill Canyon rests 
on till of Sherwin(?) age and underlies Tahoe Till; it 
has a probable age of less than 100,000 years (Dalr\'ni- 
ple, 1964b), indicating that the Tahoe Glaciation cor- 
relates with the early Wisconsin of the mid-continental 
United States. 

The Toowa N'olcanic Field, at the headwaters of 
the South Fork of the Kern River, includes several 
well-preserved basaltic cinder cones and flows along 
Golden Trout Creek, as \\ ell as two isolated s\nimetri- 
cal latite(? ) domes, Tenipleton Mountain and .Monache 
Mountain, each about 1,500 feet high (Webb, 1950). 



1966 



Batf.man and Wahrhaftig: Sikrra Nf.vada 



143 




A I luv iun 

Includes some volcanic 

rocks in lowlands 



Bithop Tuff 



Nisriy flat-lying Tartlsry rock* 

of the woitirn foot of the 

Siarri Nevada 

• *• 

Quaternary volcanic center 



Late Cenozoic fault 
Dot on dOMnthrown side 

Structure contour thoNing anount 

of lata Cenozoic deformation 

in thouetnde of feet 



Figure 10. Cenozoic tectonic map of the Sierra Nevada, showing late Cenozoic faults, late Cenozoic deformation by contours, ond Quoternory 
volcanic centers. 

Contacts from Chico sheet. Walker Lake sheet, Sacramento sheet (prelim, comp.), San Jose sheet (prelim, comp.), Fresno sheet (prelim, comp.), and 
Bakersfield sheet. Geologic Map of California, Olaf P. Jenkins edition, and from Bateman and others, 1963; Bateman, 1965; and Pokiser and others, 

1964. Contours on west slope of Sierra Nevada after Christensen, in press, 1966; contours and buried faults at south end of San Joaquin Valley 
on top of Vedder Sand (lowermost Miocene), from Richardson, 1965. Contours on Coyote Flat surface on eost side of Sierra Nevado, from Bateman, 

1965, and generalized from topography south of Bridgeport; altitudes of these contours reduced by 4,000 feet to agree with deformation datum of 
contours on west side of Sierra Nevoda. Distribution of Bishop Tuff from Gilbert, 1938; and Batemon, 1965. 



Geology of Northern California 



Bull. 190 




1966 



Baikman and Wahrhaftig: Sif.rra Nkvada 



145 



Flows along Golden Trout Creek extend to tlie floor 
of the Kern River Canyon at the south end of Sequoia 
Park. On their upper surfaces are scattered giant 
quartz-monzonite boulders which ma\- be glacial er- 
ratics and patches of gravel thought to be glacial out- 
wash, both of a pre-Wisconsin glaciation. 

lATE CENOZOIC DEFORMATION AND EROSION IN THE 
NORTHERN SIERRA NEVADA 

The evidence for the late Cenozoic deformation of 
the Sierra Nevada has recently been reviewed by 
M. N. Christensen (1966) and the discussion that 
follows draws heavily on his paper. 

It is generally agreed that the Sierra Nevada is a 
great fault block, bounded on the east by a line of 
faulting and tilted westward more or less as a unit. 
The eastern boundary is not a single great fault, but 
a series of eii echelon and branching faults, interspersed 
with ramps and arches. There is uncertainty' and con- 
trovers\' over the time of uplift and tilting, the total 
amount of uplift, and the amount of internal deforma- 
tion, if any. Stratigraphic, structural, physiographic, 
and paleobotanic evidence has been used to determine 
the amount and time of deformation. More recently 
potassium-argon dates on critical volcanic deposits 
have provided additional information on the time of 
deformation. As is clear from the preceding pages, 
the quality of information about the amount and time 
of uplift and tilting is much better for the northern 
Sierra Nevada than for that part of the range south 
of the Tuolumne River. The southern area lacks the 
extensive superjacent cover of stream gravels and vol- 
canic rocks from \\'hich estimates of uplift and tilting 
can be made, and most conclusions regarding the Cen- 
ozoic deformation of the southern part of the range 
are based on physiographic evidence, such as upland 
surfaces, valley-side benches, and knickpoints in stream 
profiles. As will be shown below, these are believed 
to be unreliable criteria for measuring deformation. 

The uplift and erosion of the Sierra Nevada north 
of the Tuolumne are treated in this section, and that 
of the Sierra Nevada south of the Tuolumne in the 
next section. 

The best evidence that the Sierra Nevada \\as tilted 
as a unit consists of the evenness of the west-sloping 
interfluves of the northern Sierra Nevada. These broad 
flat ridgecrests are the surfaces of andesitic mudflows, 
from which, in some places, overlying gravels and 
mudflows have been stripped; the\' show that the 
Pliocene andesites have suffered very little internal 
deformation. Demonstrable faults on the west side of 
the northern Sierra are remarkably few. At La Porte 
the channel of the Tertiary Yuba River has been offset 
a total of 550 feet on a northwest-trending fault zone 
about a mile wide (Lindgren, 191 1 ), the channel of the 
South Fork of the Tertiary Yuba has been offset at 
Yankee Jim about 25 feet (Browne, 1890), and the 
latite of Tuolumne Table Mountain and the andesite 
at Mokelumne Hill have been offset 100 feet or more 



on the Mother Lode fault (Eric and others, 1955; 
Cloldman, 1964). All these faults trend northwest and 
are downthrown on the northeast side. 

The cla.ssic estimate of the tilting of the Sierra Ne- 
vada is that of Lindgren (1911), who compared the 
slopes of the southw est-flowing segments of the bed- 
rock profiles of the reconstructed Tertiary rivers with 
the slopes of their northwest-flowing segments. The 
southwest-flowing segments, he reasoned, would show 
the maximum increase in gradient, whereas the north- 
west-flowing segments would parallel the tilt axis and 
therefore show no increase in gradient. By subtracting 
the gradients of the latter from those of the former, 
he could determine the amount of tilting. He found 
the southwest-directed segments of the lower courses 
of the Tertiar\' rivers to have gradients of 70 to 100 
feet per mile, and the northwest-directed segments to 
have gradients of 10 to 30 feet per mile, and by sub- 
traction arrived at an average tilt of about 60 to 70 
feet per mile, which gave an uplift along the crest of 
the range of 3,600 to 4,900 feet between the head of 
the Yuba and the head of the Mokelumne River. By 
appl\'ing this tilt correction to the north- and north- 
east-flowing segments of the South Fork of the Terti- 
ary Yuba between Yankee Jim and Dutch Flat, where 
the direction of flow indicated by sedimentar\' struc- 
tures is upslope, he was able to explain the anomalous 
present slope of these reaches. Lindgren's stud\' of the 
stream profiles remains a classic in the quantitative 
application of geomorphology to a tectonic problem. 

Hudson (1955) attempted to refine Lindgren's work 
b\' using a different method of calculation. He as- 
sumed that the bedrock profile of the South Fork of 
the Tertiary Yuba River was originally smooth, chose 
triplets of adjacent differently directed segments of 
the Tertiary bedrock profile, and solved for the direc- 
tion and amount of tilting that would give the seg- 
ments of each triplet the same slope. He adjusted his 
solutions, where necessary, to give a smooth profile 
and interpolated the slope between sets of triplets. 
Hudson's results for the Yuba differ considerably from 
Lindgren's. He concluded that there had been much 
deformation within the range and that total uplift on 
the crest amounted to less than 2,000 feet. 

Christensen (1966) has reviewed the work of 
Lindgren and Hudson and concluded that many of the 
reaches selected by Hudson were so short that irregu- 
larities in the river bottom could have seriously af- 
fected his results. Christensen determined, from a 
study of 19 modern alluvial streams of comparable 
drainage basin area, that the original slope of the al- 
luviated portions of the Tertiary Yuba should be no 
greater than 30 feet per mile, thus confirming Lind- 
gren's major premise. 

In considering the calculations of both Lindgren 
and Hudson, it is well to recall that the accumulation 
of 500 feet of prcvolcanic gravels in the middle reaches 
of the Tertiary Yuba River implies either a rise in base 
level or a backward tilting of the drainage basin, prob- 



146 



Geology of Northern California 



Bull. 190 



r BOOO 


> 
w 






2 


00 

a 

1 oi^lll. 




m 




< 
> 






m 

u 


1 ^__i--iyi^--' 




__^ — ■" 


- 4000' 




1 






j;Moii£iA^ 


::;;:i^J^^^---;=^^^5?f^'^'^^'^^^^ 






















,, 




._^. 


.^-- 


-.s-^- — "^ 






, 




























fliv«r 






2000' 








Horth__ 


_ ^ Aaeri^on 

^ 






Sta lival 










12 3 


4 


9 III !•• 









Figure 12. Projection of prevolcanic (Eocene?) and intervolcanic (Pliocene) channels of Forest Hill Divide, and of the North Fork of the American 
River, onto a vertical plane striking N. 50° E. Data from Ross E. Browne, 1890. For location of projection plane see figure 10. Vertical exaggeration 
about 10 X. 




PROJECTION PLANE N. 50° E. 

I 2 3 4 5 II Ik 



Figure 13. Projections of two volcanic toble mountains of the western Sierra Nevada. A. Projection of Tuolumne Table Mountoin onto o verticot 
plone striking N. 40° E. Geology modified from Taliaferro and Solori, 1949; Eric and others, 1955; and Big Trees Folio. B. Projection of Little Table 
Mountain ond the basalt of Table Mountoin on the San Joaquin River onto a vertical plane striking N. 50° E. Geology modified from Mocdonold, 
1941, and original surveys. For location of projection planes see figure 10. Vertical exaggeration about 10 X. 



i: 



1966 



Batf.man AM) W'aiirhaftk;: Sikrra Nf.vada 



147 



ably both. Lindgren's explanation of the aggradation 
as due to constriction of the valley at Smartsvillc seems 
untenable, for it fails to explain how the valley up- 
stream from Smartsville was cut in the first place. Only 
the Tertiary Yuba-channel shows this evidence of back 
tilting or rise in base level — the other streams did not 
aggrade their beds in prevolcanic times. Hence, in 
earl\- Tertiary time, there was probably a differential 
sagging of the crust beneath the Sierra, localized in 
the Yuba drainage; this sagging may have amounted 
to 500 feet. The total uplift and tilting after the depo- 
sition of the volcanic rocks was the amount calculated 
by Lindgren, plus whatever downward displacement 
took place during the accumulation of the gravels. 
Part of the discrepancy between Hudson's and Lind- 
gren's conclusions may arise from this period of 
deformation. 

The present drainage of the northern Sierra Nevada 
was undoubtedly consequent upon the surface of the 
volcanic rocks. The pattern of southwest-flowing 
streams was developed over a long period, as succes- 
sive channels were filled and buried b\' volcanic mud- 
flows and streams were forced to shift to new courses. 
The present courses are essentially those the streams 
possessed at the end of the period of volcanic erup- 
tions, modified by changes resulting from superposi- 
tion onto bedrock structures that were oriented 
normal to the streams. During uplift and tilting the 
rejuvenated streams deepened their channels, so they 
now flow in narrow V-shaped canyons several hun- 
dred to as much as 3,000 feet below the floors of the 
prevolcanic channels. Part of the Tertiary cover was 
stripped from the relatively flat interfluves, and large 
areas of the early Cenozoic topography have been ex- 
humed (see fig. 7). Thus the present topography of 
the northern Sierra Nevada consists of elements of 
three diff^erent ages: prevolcanic topography that was 
never buried or has been exhumed from beneath the 
volcanic cover; younger, relatively plane surfaces de- 
veloped on the volcanic rocks; and steep modern can- 
yons, incised into both volcanic cover and bedrock. 

Lindgren (1911) and others have stressed that the 
tilting was initiated at the beginning of the volcanic 
eruptions. They base this on the assumed rejuvenation 
of the streams shown by the steep walls of the inter- 
volcanic channels, and by the coarse andesitic cobbles 
of the intervolcanic gravels. The steep canyon walls 
and coarse gravels probably reflect the character of 
the well-jointed andesitic rocks rather than any 
change in the gradient of the streams. 

Axelrod (1957) has shown that the floras of Mio- 
cene age from the \'alley Springs Formation and of 
Pliocene age from the overlying andesites and from 
their equivalents in west-central Nevada both indicate 
the same climate, and that they do not indicate the 
existence of a rain shadow, such as the one now pres- 
ent east of the Sierra Nevada. He estimates from the 
distribution of floras that in Miocene and earlv Plio- 



cene time tlic mountains near Lake Tahoe could not 
have been higiier than 2,000 to 3,000 feet, and there- 
fore that the crest of the range has been subsequently 
uplifted 5,000 to 6,500 feet. 

Reconstruction of the intervolcanic profiles and 
comparison with the prevolcanic profiles (see fig. 12) 
show s that at least in the lower and middle reaches of 
the Sierra Ne\ada the intervolcanic profiles are essen- 
tiall\- parallel to the prevolcanic profiles and at the 
same altitude. 1 he profiles of the Forest Hill Divide 
(fig. 12), constructed from data in the map of Ross E. 
Browne (1890), show the intervolcanic channels to be 
at most only 100 feet below the prevolcanic channels, 
in spite of the fact that they were much closer to the 
mouths of the streams. Similarly, the Cataract Chan- 
nel of Table Mountain, in Tuolumne and Calaveras 
Counties, which also has a more direct course to base 
level than the prevolcanic channel, actually overlies 
the prevolcanic gravels in the vicinity of Vallecito 
and Douglas Flat (Turner and Ransome, 1898). There 
seems to be no reason to infer from the slopes of the 
intervolcanic channels that the northern Sierra Nevada 
was tilted before the channels were cut. 

Three major en echelon zones of comple.x gravity 
faults border the Sierra Nevada on the east between 
Mohawk \'^alley and Sonora Pass. The northernmost 
of these extends southeast from Mohawk Valley and 
the west side of Sierra \'^alley, through Donner Lake, 
and along the west side of Lake Tahoe. Its displace- 
ment is about 3,000 feet at Mohawk Valley, more than 
2,000 feet north of Donner Lake, and is indicated by 
physiographic evidence to be as much as 5,000 to 
6,000 feet west of Lake Tahoe (Birkeland, 1963; Dur- 
rell, this bulletin). East of this fault zone and separated 
by upwarped blocks are the tectonic depressions of 
.Mohawk, Sierra, and Truckee Valleys, and Lake 
Tahoe (Birkeland, 1963). East of the Tahoe and 
Truckee depressions lies the north-trending uplift of 
the Carson Range, which joins the Sierra Nevada south 
of Lake Tahoe. 

The Carson Range is a complex horst, w-hich passes 
at its northern end into a broad anticlinal arch 
(Thompson and White, 1964). It faces Washoe and 
Carson V^alleys on the east by magnificent fault scarps 
that reach a height of 4,000 to 5,000 feet east of the 
southern part of Lake Tahoe. The total displacement 
is about 8,000 feet. The line of faults branches south- 
ward as it enters California, and the branches continue 
into the Sierra Nevada and die out near the range 
crest (Curtis, 1951; 1965). 

Carson Valley, to the east, is apparently the de- 
pressed side of a tilted fault block whose uplifted 
eastern part is the Pine Nut Range. This block rises 
southward, and where it crosses the state line into 
California it becomes continuously mountainous and 
merges with the Sierra Nevada. The third zone of 
complex faults is on the east side of this block, and 
makes the escarpments on the west side of Antelope 



148 



Gkologv of Nouthfrn Cm, ikornia 



Bull. 190 



2000 



Ribbon 


C 


^ 




ree k 




- 






o..^'> "^^ Rocks ^^ ^^ 

R'bbon , \: . /~^v/ ^ 


- 






^"--^ \ 4,6 0" — 1 feMdolv'ei/ 


. 


















^^ \ J 1 Falls 


- 
















\ / 








... , , \ Merced R / 


" 






' '2,900' 



Figure 14. Projection, on a north-south plane, of cross profile of Yosemite Valley between El Capitan ond Cathedral Rocks (solid line) ond of 
profiles of Ribbon and Bridalveil Creeks (dashed lines). Elevations of the Merced River of the Broad Valley Stage (6,700 ft). Mountain Valley Sloge 
(5,800 ft), ond Canyon Stage (4,800 ft) of downcutting, and the profiles on which they are based (dot-dashed lines), ore from Molthes (1930, fig. 27, 
p. 87). Bedrock surface from Gutenberg, Buwoldo, and Sharp (1956, fig. 8, p. 1072). No vertical exaggeration. Reproduced from Wahrhaftig, 
1962, p. 38. 




SEA LEVEL 



40 60 eo 100 MILES 

Figure 15 Longitudinol profile of the Merced River (after Hudson, 1960, p. 1 551 -reproduced from Wahrhaftig, 1962, fig. 3, p. 37). 



1966 



Bateman and Wahriiauk;: Sierra Nevada 



149 



and Slinkard Vallevs. Displacements on the faults on 
each of these escarpments are 2,000 to 2,500 feet 
(Curtis, 1965). 

Birkeland (1963) and Dalrymple (1964a) have 
show n that the bulk of the movement along the faults 
west of Truckee \'alley took place after the eruption 
of an andesite that is 7.4 million \ears old and before 
the eruption of the earliest of the flows of the Louse- 
town Formation that is 2.3 million years old. The old- 
est of the Lousetown flows is displaced as much 
as 700 feet along outlying segments of this fault zone, 
and even the Noungest of the Lousetown flows, 
which is 1.3 million years old, has been offset and 
tilted. 

Deformation of the Carson Range began in middle 
Pliocene time, during the accumulation of the ande- 
sites (Thompson and White, 1964), and no more 
than 400 feet of deformation and downcutting has 
occurred since the deposition of the Lousetown flows 
a little more than a million \ears ago. That deforma- 
tion along the major faults is continuing is indicated 
b\- fresh slickensided fault scarps exposed at Genoa, 
in Carson Valley at the east foot of the Carson Range 
(Lawson, 1912). 

According to Curtis (1951; 1965) the fault systems 
in the headwaters of the Carson River and Antelope 
Valley had two periods of activity- since the eruption 
of the andesitic mudflows in middle Pliocene time. 
These were separated by a period of quiescence during 
which a surface of relatively low relief was carved 
across the areas. 

LATE CENOZOIC DEFORMATION AND EROSION IN THE 
SOUTHERN SIERRA NEVADA 

In the absence of the extensive Tertiarv cover that 
made possible the measurement and dating of uplift 
in the northern part of the range, geologists working 
the Sierra Nevada south of the Tuolumne River have 
had to rely on physiographic criteria of uplift. The 
physiographic features used are of three kinds: summit 
uplands and benches, assumed to be remnants of an- 
cient surfaces of low relief formed near base level; 
profiles of the assumed Tertiary streams, reconstructed 
from knickpoints on their tributaries; and steep escarp- 
ments, assumed to be fault scarps. 

In 1904 Lawson described extensive benches and 
summit uplands on granitic rocks at the head of the 
Kern River, and he assumed these were remnants of 
erosion surfaces of low relief formed close to sea level. 
He named r\vo main surfaces the Subsummit Plateau, 
11,000 to 12,500 feet high, and the High \'alley, 6,500 
to 10,000 feet above sea level. On the basis of the rela- 
tive amounts of erosion involved, Lawson estimated 
that the cutting of the Kern Can\on into the High 
Valley surface took 300 times the length of the post- 
glacial period (which he estimated to be about 1,000 
years long), and the cutting of the High Valley took 
2,400 times the length of post-glacial period. Using 
modern knowledge of the time since the disappear- 



ance of the glaciers, these estimates become 3 million 
and 24 million vears respectively. 

Knopf (1918) extended the mapping of Lawson's 
surfaces northward along the cast side of the range to 
the Bishop Creek area. Matthes (1937) refined Law- 
son's history, and recognized three levels of summit 
flats and benches, and hence four stages of uplift at 
the headw atcrs of the Kern. The two highest surfaces, 
vertically about 1,000 feet apart and together cor- 
responding to Law.son's Subsummit Plateau, Matthes 
named the Cirque Peak Surface and the Boreal Plateau 
Surface. A surface about 2,000 feet lower, correspond- 
ing to Lawson's High \'alle\-, he named the Chagoopa 
Surface; and the final stage of erosion he named the 
canyon-cutting stage. Alatthes' estimates of the dura- 
tion of these stages were 1 million years for the cutting 
of the canyon, 10 to 15 million \ears for the Chagoopa 
cycle, 20 million years for the Boreal Plateau cycle, 
and 5 to 10 million years for the Cirque Peak cycle. 

More recently, A.xelrod (1962; A.xelrod and Ting, 
1961) has attempted to date the uplift and cutting of 
the Chagoopa Surface by a studv of pollen grains 
embedded in sediments l\ing on that surface and in 
vertebrate-dated sedimentary rocks in the Owens \'al- 
le\- graben east of the Sierra Nevada. He concluded 
that the Chagoopa Surface is middle Pleistocene ( Kan- 
san) in age, and that the bulk of the uplift of the 
Sierra Nevada took place in Pleistocene time. 

Using the second type of ph\'siographic evidence, 
stream profiles, Matthes (1930) noted that the upper 
reaches of lateral tributaries of the .Merced River flow 
with gentle gradient in broad shallow valleys to an 
abrupt knickpoint, from which their lower courses 
cascade to the Merced River incised in a narrow can- 
non several hundred to 3,000 feet below (fig. 14). By 
projecting the gentle gradients downstream to where 
the tributaries joined the Merced, he defined a series 
of points marking the bed the river occupied before 
the uplift and rejuvenation responsible for the knick- 
points, and by connecting these points he could re- 
construct the present position of the profile of the 
Tertiary Merced River. Furthermore, .Matthes found 
that many of the streams had two knickpoints, and 
was able to reconstruct two ancient profiles: the older 
he called the Broad \'alle\- stage and placed in the 
Miocene; and the other, the Mountain X'alley stage 
and placed in the Pliocene. He calculated that since 
the end of the Broad \'alley stage the tilting of the 
Sierra Nevada amounted to about 70 feet per mile and 
the crest of the range, w hich formerl\- was about 4,000 
feet high, had been uplifted 9,000 feet. Hudson (1960) 
extended iMatthes' profiles to the San Joaquin \'alley 
(see fig. 15), and from them estimated that the uplift 
at the crest amounted to onl\- 4,000 feet. 

iMatthes ( 1960) later carried this type of analysis into 
the San Joaquin Basin, where the Miocene and Plio- 
cene profiles of the San Joaquin River were also re- 
constructed from tributary knickpoints. Here, how- 



ISO 



Gkoi.ogy of Northern California 



Bull. 190 




Photo 13. Distant view of Yosemite Valley, looking east. El Copitan is the white cliff on north side of the valley. Cathedral Rocks are on the 
south side of volley, opposite El Capiton, with the steep gorge of Bridalveil Creek in front of them. The shadowed face of Half Dome is above and 
left of El Capiton. The flat light-colored area in lower right is Big Meadow. Bigoak Flat Road, in left foreground, is along a step front; a second 
and higher step front extends as a series of granite domes ond cliffs diagonally to the left from near El Capiton. 

On the skyline at left ore Tioga Pass and Mount Dona. In front of Mount Dona ore sharp peaks of Cathedrol Peak Granite on the near side of 
Tuolumne Meadows. On the central skyline behind Yosemite Valley ore the White Mountains, lying east of the Owens Valley Groben. The darker 
peaks of the Sierra crest between Yosemite Volley and the White Mountains Include Mount Lyell and the Ritter Range. On the skyline on right are 
the mountains around the head of the San Joaquin Basin. U.S. Geological Survey photograph GS-OAhl-3.17. 



ever, this analysis breaks down, for Matthes' Miocene 
and Pliocene profiles are not parallel to the ancient 
stream profile defined b\- the basaltic lavas of Table 
Mountain. 

The numerous west-facing escarpments in the south- 
ern Sierra Nevada were identified by Hake (1928) and 
Matthes (1950; 1964) as fault scarps. The flat benches 
and mountain tops behind the .scarps were assumed to 
be offset segments of an originally continuous surface. 
This explanation was given plausibilit\- by the exist- 
ence of the famous Kern River fault with its erosional 
fault-line scarp facing the Great Valley at the south 
end of the range (Blackwelder, 1928; Gilbert, 1928). 
Birman (1964), on the other hand, regarded these 
escarpments as backwasting mountain fronts and the 
benches between them as piedmonttreppen. 

The foregoing analyses failed to take into account 
many of the essential topographic features of the 
southern Sierra Nevada — features that were not 
readily apparent until the publication of the U.S. Geo- 



logical Survey topographic maps at a scale of 1:62,500. 
The western slope of the Sierra Nevada south of the 
Tuolumne River gains altitude b>' a series of giant 
west-facing steps, which have risers from 100 to sev- 
eral thousand feet high and treads a few hundred 
feet to several miles across. These steps are irregular 
in height and map pattern. The risers (or fronts) have 
abundant outcrops, while most treads are underlain 
by deep gruss (over 100 feet thick in places) and 
slope back toward the next higher front (fig. 16), so 
that minor tributaries commonly flow parallel to the 
fronts. Most streams cascade down the fronts in short 



Figure 16 (opposite). Mop of stepped topography of the Sierra 
Nevada south of Tuolumne River. 

Step fronts compiled from 1:62,500 topographic mops. Geology from 
Burnett and Mathews, 196 ; Smith, 1965; Wohrhoftlg, 1965e, figure 4; 
Botemon, 1965a, 1965b, 1965c; Huber ond Rinehort, 1965; Peck, 1964; 
Botemon and others, 1962; and N. King Huber, written communico- 
tion, 1966. 



1966 



Bateman and Wahrhaftig: Sierra Nkvaua 



151 






■i Lake 




Qual 8 ma ry a I luv i urn 



Area covered by 
Wisconsin gtaciation 



Tertiary ma r i ne 
and conlinental 
sad i men t a ry r ocKs 



Stap fronts Rusged areas Crest ot the 
of steep si ope Sierra Nevad 



35°30 



152 



Geology of Northkrn Calikorma 



Bull. 190 




Photo 14 (above) 
fine examples of the 
Bare granite domes 
Their origin may b 



Fuller Buttes 
nany domes in granitic roi 
uch OS these weather and 
port to processes 



lilar to tho 



ely slowly 



occount for the stepped topography. Phofogroph by N. King Huber. 

boulder-choked canyons and cross the treads with 
graded sandy streambeds. Steps are found not only 
facing the San Joaquin \^alley but also lining the can- 
yons of the San Joaquin, Kings, and Kern Rivers. 

According to Wahrhaftig ( 196.ie) these steps are 
the eventual landforni resulting from the fact that soil- 
covered granite weathers much more rapidlv to grass 
than does exposed granite, because the buried granite 
is in contact most of the year with water and organic 
decay products w hile the surfaces of the e.xposed gran- 
ite dry shortly after each rain. Because granite where 
widely jointed cannot be eroded until it is weathered 
to gruss, exposures of solid rock act as local base levels 
for erosion of the still buried rock upstream or up- 
slope. The exposures grow to lines of outcrops, which 
grow into escarpments — the step fronts — through low- 
ering of the country downstream from them. 

The fixing of streams in bedrock notches from 
which the\- cannot migrate, and the establishment of 
bedrock outcrops at all low points on the crest of a 
step front, may involve much lateral migration and 
drainage capture. Once established, however, the 
growth of the stepped topograph)- is inevitable because 
the country upstream from each bedrock notch can be 
flattened to the level of the notch but not below it. 




Photo 15. Unloading joints, spaced 2-5 feet apart, exposed by 
glacial quorrying on the side of a dome in granitic rocks. Northeast 
side of Chiquilo Ridge, Shuteye Peok quadrangle. For an early discus- 
sion of their origin see Gilbert, 1904. Phofogroph by N. King Huber. 



1966 



Bate.man and VVahrhaftk;: Sikkra Nkvada 



153 




Photo 16. View south down Kern Canyon from near the mouth of Whitney Creek, Sequoia Notional Park. The mount 
Red Spur, and forested f>at area behind it is Chogoopa Plateau, a little over 2,000 feet above the floor of Kern Cony 
in the center of the forest is Sky Parlor Meadow. Behind the Chagoopo Plateau the peaks of the Great Western Divide cic 
Canyon. The bench above the canyon rim on the left is correlated by Lawson ond Matthes with the Chagoopo Plateau, 
timberline near the left margin is the Boreal Plateau, with Funston Lake forming o dork oreo in its center. Beyond the B 
of Golden Trout Creek and the slightly glaciated peaks of the Toowo Range. Mountains on skyline ore the southern Sierr 
Greenhorn Mountains, and on the extreme right, Mount Pinos and the San Emigdio Mountains lying beyond the south end 

The remarkable straightness of the Kern Canyon, which is eroded along an inactive fault zone, is evident in this vie 
Chagoopo surface is found only at the head of the Kern Canyon. U.S. Geological Survey photograph GS-OAL-1-73. 



oin in r 


ght 


oregrou 




on. The 


light 


colored 


oreo 


se south 


word 


toward 


Kern 


The ftot 


bore 


area a 


bove 


oreol Plo 


teou 


is the V 


alley 


3 Nevod 


a, Te 
n Jo 


lochopi. 


ond 


3f the So 


aquin V 


alley. 


W, OS is 


the 


fact tho 


t the 



The characteristics of stepped topography which 
may be used to identify the process are: (1) the ir- 
regular height and map pattern of fronts; (2) the back- 
ward slope of the treads (flat mountain-tops that are 
treads are slightly dished); (3) variation in number and 
altitude of knickpoints from stream to stream, even 
on tributaries to the same master stream; and (4) lack 
of parallelism of summit flats and benches, or of stream 
profiles reconstructed from knickpoints, with strati- 
graphically defined surfaces. Broad benches may exist 



at the headwaters of a stream system and be lacking 
at the appropriate height downstream. 

Most of the benches and escarpments of the granitic 
terrane of the southern Sierra Nevada have the char- 
acteristics enumerated above. In particular, the rem- 
nants of the Chagoopa Surface at the head of Kern 
River do not extend downstream below the mouth of 
Golden Trout Creek, and as the walls of the Kern 
Canyon close in for several miles below this creek no 
equivalent of the Chapooga Surface is possible. Where 



154 



Gf.ology of Northern California 



Bull. 190 



benches appear along tlic Kern farther downstream, 
thev are either much lower or much higher than the 
level defined b\' the Chagoopa Plateau. 

According to the hypothesis of origin presented 
above, the steps can originate from a variety of causes 
at any altitude, and the treads therefore probably lack 
geomorphic significance as remnants of old-age sur- 
faces. Many of the remnants of the supposed Boreal, 
Chagoopa, Broad \'aliey, and Mountain Valley sur- 
faces are thought by Wahrhaftig (I965e) to be treads 
in the stepped topograph)', and many of the knick- 
points used by Matthes in reconstructing his profiles 
on the Merced and San Joaquin Rivers are thought 
to be knickpoints in the stepped topography. Thus 
the Broad Valle\' and Mountain Valley profiles, if 
valid, are probably valid only in a general way. 

The validit)- of the strictly physiographic criteria 
of uplift is therefore in doubt, and the\' cannot be used 
alone but must be supplemented with stratigraphic 
evidence. Some stratigraphic evidence exists within the 
range, as for example the basalt flows of Table Moun- 
tain on the San Joaquin, but most of the available 
stratigraphic evidence lies buried in the filling of the 
San Joaquin V^alley, and its bearing on uplift within 
the range is indirect and involves many assumptions. 
The stratigraphic evidence must be evaluated in the 
light of the overall shape of the range, which toward 
the south departs from the simple asymmetric profile 
with an even westward-slope characteristic of the 
northern Sierra Nevada. South of Yosemite, subsidiary 
ridges whose height approaches that of the main crest 
are found progressively closer to the Great \'alley the 
farther south one proceeds. At the south end of Se- 
quoia Park, crestlines in the eastern half of the range 
are at about the same altitude over a width of 25 to 
30 miles and the western half of the range slopes west- 
ward at an angle of about 4° from mountains that are 
9,500 feet high, and only 25 miles from the Great 
\'alle\- floor. This regional change in present overall 
shape implies a fundamental difference in the pattern 
of Cenozoic deformation; the northern part is tilted, 
whereas in the southern part a block, bounded by a' 
flexure that sharpens southward, is bodily uplifted 
(Christensen, 1966). 

The basalt-capped channel of Table Mountain on 
the San Joaquin River rises toward the northeast at 
130 to 140 feet per mile (1°30'); this surface, pro- 
jected eastward, coincides roughly with broad benches 
at about 7,000 feet in altitude and 3,000 feet above 
river level at the forks of the San Joaquin, 45 miles 
northeast of the Great V^alley. Similarly, the basalt 
remnants along the Kings River rise eastward at about 
140 feet per mile. If these streams had gradients of 
30 feet per mile, as did the Tertiary streams in the 
northern Sierra Nevada, tilting of the western part 
of the range in the last 9.5 million \ears (the age of a 
basalt correlated with that on Table .Mountain) has 
amounted to about 1 10 feet per mile, resulting in about 
5,000 feet of uplift at the forks of the San Joaquin. 



At the south end of the range, between the Kern 
and White Rivers, marine and continental sediments 
of Miocene age along the west base of the Sierra Ne- 
vada dip 5° to 6°3r westward (Pease, 1952; Sperber, 
1952). The eastward projection of the base of the 
Tertiary section at these dips barely clears the tops 
of the highest peaks for 10 to 15 miles into the range, 
and then rises above the tops of peaks to be about 
2,000 feet above the crest of the Greenhorn Moun- 
tains, 25 miles east of the Tertiary outcrops. Farther 
east, the summit of the Sierra Nevada flattens. 

These fragments of data from within the range sug- 
gest that the southern Sierra Nevada was tilted along 
its western margin from 1°30' to 5° westward during 
the Pliocene, the dip decreasing eastward into the 
range and increasing southward along the west flank 
of the range. In response to this tilting and uplift, 
the San Joaquin, Kings, Kern, and other rivers deep- 
ened their canyons, cutting their inner gorges. The 
previousK- cited evidence of the San Joaquin sug- 
gests that this deepening affected its upper reaches 
about 3.5 million \ears ago. Evidence on the Kern, 
also cited above, suggests that the canyon of that 
stream was cut nearly to its present depth by 3.5 mil- 
lion \ears ago. 

The basalt of Table Mountain, and the basalts in 
the Kings River drainage, impose severe restrictions 
on the amount of erosion resulting from this uplift, 
since they define valle\-floor profiles onl\' 2,000 to 
4,000 feet above the floors of the present narrow can- 
yons. The volume of sediment represented by the 
post-Pliocene canyons was estimated by filling these 
parts of relief models of the Fresno and .Mariposa 
(1:250,000) Arm\- .Map Service sheets with sand, and 
measuring the volume of the sand. The total volume 
eroded from beneath this surface on these two quad- 
rangles was found to be 500 cubic miles, representing 
an average lowering of the surface of the Sierra Ne- 
vada in these two quadrangles of about 300 feet. 

The lone outcrops of Little Table Mountain west 
of Friant give a measure of the tilting of the Sierra 
Nevada since Eocene time. .Macdonald (1941) shows 
dips of 3° or about 250 feet per mile on these rocks. 
Janda (oral communication, 1965) has found, on the 
other hand, that the upper surface of Little Table 
.Mountain slopes westward at the same angle as the 
surface of Table Mountain east of Friant, and pro- 
jected eastward to Big Table Mountain, is about 500 
feet higher. He regards the bedding w ith the steeper 
dips measured bv Macdonald as possibl\- deltaic fore- 
scts. If Janda's interpretation is correct, there was no 
tilting during the interval between the Eocene and 
Pliocene, but onlx- relative lowering of base level of 
about 500 feet. 

The slope of stratigraphic surfaces beneath the 
Great X'alley could be projected eastward into the 
Sierra Nevada to get a measure of tilting and uplift 
during various intervals within the Cenozoic. The re- 
sults of a comparison of slopes calculated from well 



1966 



Batf.man and VVahrhaftig: Sikrra Nkvada 



155 



TABLE 1. Comparison of dip of formations beneath the San Joaquin Valley with the west slope 
of the Sierra Nevada, in feet per mile. 





Location and reference to cross section 




Chowchilla-Dos Palos: 

Union Gamble 7-15 to 
Pure Oil Chowchilla 1 
(Bowen, 1962, pi. IS) 


Reedley-Coalinga : 

Superior White 1 to 

Amerada Lawton 58-26 

(Church, Krammes, and others, 

1957b) 


Bakersfield: 

Bald Eagle 74 to 

Western Gulf, KCL B-45 

(Church, Krammes, and others, 

19S7a) 


Base of the Pliocene 




140 


540 


Base of the Miocene 


103 


230 


975 (also basement) 


Base of the Eocene 


119 


235 




Upper surface of basement 


336 


400 


(975) 


Slope of Pliocene 
basalt in Sierra Nevada 


140 

(San Joaquin) 


140 

(Kings River) 




Slope of western Sierra Nevada along 
line east of section 


240 


270 


450 



data with the slope of the surface generalized from 
summit altitudes in the western Sierra Nevada are 
shown in table 1. From this table it is seen that the 
slope of the base of the Pliocene agrees reasonably 
well with the slope of San Joaquin Table Mountain, 
and that the generalized slope on summit altitudes 
corresponds to the slope at the base of the Eocene 
in the central San Joaquin Valley and with the slope 
of the base of the Pliocene in the southern San Joaquin 
Valley, and is about Yz to 73 the slope of the top of 
the basement. If the assumption that there is no dif- 
ference in tilting from the eastern Great Valley to 
the Sierra Nevada can be made, and if we assume 
that the depression of the valley was matched by a 
corresponding rise in the Sierra, then there was little 
tilting of the Sierra Nevada during Eocene and Oligo- 
cene time, about 90 feet per mile of tilting during 
Miocene time, and about 140 feet per mile of tilting 
during Pliocene time, in the vicinity of the Kings and 
San Joaquin Rivers. Farther south, near Bakersfield, 
the tilting was much greater. 

In the southern Sierra Nevada, as in the northern 
part of the range, the east side is predominantly a zone 
of gravity faulting. From Antelope V^alley southeast to 
Big Pine the east-facing range-front faults have an e?i 
echeloii pattern, as they do in the north, and alternate 
with ramps and arches. This pattern is interrupted by 
two large roughly equidimensional volcano-tectotuc 
depressions — Mono Basin and Long Valley. From Big 
Pine south to Owens Lake the displacement, totalling 
14,000 to 19,000 feet, is along two parallel east-facing 
faults from 5 to 7 miles apart. Near Owens Lake they 
converge and continue southward as a single fault 
zone, which terminates at the Garlock fault near Te- 
hachapi Pass. 

Between Antelope Valley and Mono Basin range- 
front faults are inconspicuous. The triangular Bridge- 
port Valley, at the east base of the Sierra in this stretch 



of the front, may be a deep alluvial basin bounded by 
faults, but elsewhere the range merges with mountains 
to the east. North of Bridgeport Valley, the Sweet- 
water Mountains, which are a north-trending range on 
the east side of Antelope Valley, continue southward 
along the east side of the West Walker River and 
merge indistinctly with the Sierra Nevada to the 
south. Within the Sweetwater Mountains, Cenozoic 
volcanic rocks are complexly faulted against a granitic 
and metamorphic basement, but the faults die out 
southward and none occur at the crest of the Sierra 
Nevada. Between Bridgeport Valley and the Mono 
Basin, the east front of the Sierra Nevada, which 
slopes gently eastward toward the Bodie Hills, is ap- 
parently a ramp broken b\' antithetic faults. 

The volcano-tectonic Mono Basin is a roughly tri- 
angular depression about 30 miles long in a northeast- 
erly direction and 20 miles wide along its southwest 
side, which is the eastern escarpment of the Sierra 
Nevada. Mono Lake lies at the base of the escarpment, 
and altitudes on late Pleistocene shorelines suggests 
that the basin floor has recently been tithed down to 
the west. A pronounced steep-sided gravity low that 
lies over the central part of the basin is interpreted by 
Pakiser, Press, and Kane (1960) to represent 18,000 
± 5,000 feet of low-density sedimentary and volcanic 
deposits of late Cenozoic age. 

Long Valley is another volcano-tectonic depression 
about 15 miles south of Mono Lake (Pakiser, Kane, 
and Jackson, 1964). It is about 20 miles long east and 
west, 10 miles wide, and it makes a re-entrant into the 
east front of the Sierra Nevada. The valley is floored 
with lake sediments, alluvium, and volcanic deposits 
of late Cenozoic age (Rinehart and Ross, 1957; 1964; 
Doell, Dalrymple, and Cox, 1966; Huber and Rinehart, 
1965a,b). Its south margin is an east-trending fault scarp 
in basement rocks nearly 4,000 feet high, and its north- 
east margin is a fault scarp 2,000 to 4,000 feet high 



156 



Geology of North f.rn California 



Bull. 190 




Photo 17. Eastern escarpment of the Sierro Nevada in the vicinity of Lone Pine and Mount Whitney, seen from over the north end of Owens 
Lake. Subsidiary fault scarp lies along the east side of the Alabama Hills in the middle distance. Lone Pine is just off the picture on the extreme 
right, at the point where Lone Pine Creek emerges from the Alabama Hills. Mount Whitney is the high peok at the north end of a serroted ridge at 
the head of the conyon of Lone Pine Creek. The alluvial and outwash fan apron olong the base of the great scarp portly buries the Alobomo Hills 
on the right, and toward the left where the two fault systems merge it is faulted, cut by lokeshores, ond dissected. Late 19lh century shores of the 
now dry Owens Lake in the foreground. Owens River on the right. Total relief in this picture, from Owens Lake (3,560 ft) to Mount Whitney (14,496 ft) 
is nearly 11,000 feet. U.S. Geological Survey photograph GS-OAI-5-18. 



exposing late Tertiary volcanic rocks resting on a 
granitic basement (Gilbert, 1941). To the west and 
northwest it is overlapped !)>■ a volcanic field extend- 
ing from the Mono Craters through Mammoth Moun- 
tain, and to the southeast it is flanked by the Bishop 
Tuff. A pronounced gravity low underlies the valle\- 
and is interpreted by Pakiser, Kane, and Jackson 
(1964) to represent 18,000 ± 5,000 feet of light late 
Cenozoic volcanic and scdimcntar\- rocks, in fault 
contact with basement rocks. The boundary faults are 
curved, adding weight to the interpretation of vol- 
cano-tectonic collapse. 

The two volcano-tectonic depressions arc closel\- 
associated with Quaternar\- volcanic rocks and subsi- 
dence of the depressions with concommitant volcanism 
and infilling of the basins might have taken as much 
as 2 to 3 million years. Hot springs and Recent vol- 
canos on the floors and margins of both depressions 
show that volanic activity has not ceased. 



The east-facing Hilton Creek fault extends south 
from Long Valley for 10 miles into the Sierra Nevada, 
and has at least 3,500 feet of vertical displacement at 
McGee Mountain (Rinehart and Ross, 1964). It is the 
\\ esternmost of three en echelon fault zones that make 
the east face of the Sierra Nevada south of l-ong 
\'alley. 

Six or eight miles to the east, a second fault makes 
the great east-facing escarpment of Wheeler Crest and 
,\lount Tom. This fault has a displacement at its north 
end of as much as 7,000 feet, and extends 20 to 25 
miles south, with continuousl\- decreasing displace- 
ment, to die out in the headwaters of the South Fork 
of Bishop Creek ( Batcman, 1965). The north-facing 
mountain front between these faults is a steep ramp 
broken by numerous antithetic faults downthrown to 
the south (Rinehart and Ross, 1957). 

The broad arch of the Coyote Flat warp, east of 
the Wheeler Crest fault, breaks the continuity of 



1966 



Bate.man AM) Waiiiuiai- lie: Surra Nivada 



157 



range-front faults betw ecn Round \'allc\- and Big Pine 
(Bateman, 1965). The mountain front here is appar- 
entl\' an erosion surface of relatively low relief, de- 
formed into a broad anticline plunging to the north- 
east. The north flank of this arch slopes about 1,000 
feet per mile northward across Bishop Creek to a 
shallow east-trending synclinal axis l\'ing between the 
Tungsten Hills and the Bishop Tuff of the V^olcanic 
Tableland. Its east flank slopes from 1,600 to less than 
1,000 feet eastward toward the floor of Owens \'alley; 
gravity studies indicate that the eastward slope of the 
basement continues at the same gradient beneath the 
valley floor to the base of a concealed fault along the 
west flank of the White .Mountains. Numerous small 
antithetic faults break the continuity of this eastward 
slope. 

A few miles north of Big Pine the Coyote Flat arch 
is broken by an east-facing fault, which passes along 
the west margin of the alluvial floor of Owens Valley 
just west of Big Pine and extends farther south, cutting 
through and off^setting the basaltic volcanoes of Crater 
Mountain and Red Mountain. The displacement on 
this fault increases to the south, as indicated by grav- 
it\- gradients across it (Pakiser, Kane, and Jackson, 
1964). South of Red Mountain, it lies at the base of 
the great alluvial fan apron forming the east front of 
the Sierra Nevada, and passes along the east flank 
of the Alabama Hills to the west side of Owens Lake. 
Its vertical displacement at the Alabama Hills, calcu- 
lated from gravity anomalies, is about 8,000 feet. The 
surface breakage of the Lone Pine earthquake of 1870 
was concentrated along this fault. 

The great escarpment of the Sierra Nevada, lying 
a half dozen miles west of this fault, probably marks 
another fault, whose displacement, as indicated by 
topographic relief, may be 7,000 to 9,000 feet. South 
of the latitude of Lone Pine the escarpment bends to 
the east to approach the fault on the east side of the 
Alabama Hills, and the two faults merge just west of 
Owens Lake to form a single complex fault system 
with a total displacement on the order of 15,000 feet 
(Pakiser, Kane, and Jackson, 1964, fig. 15). This fault 
zone has been traced south\\ard to its junction with 
the Garlock fault (Smith, 1965; Jennings and others, 
1962). 

Deformation along the eastern boundar\' zone ap- 
parently began about 10 million \'ears ago, and has 
continued to the present. Judging from potassium- 
argon dates obtained for volcanic rocks associated 
with the fault scarps and warps, most of the defor- 
mation took place in the last 3 million years, and much 
of it happened in the last 700,000 \ears. Glacial mo- 
raines of Wisconsin age, which are only 10,000 to 
100,000 years old, are offset as much as 50 feet by 
range-front faults. 

A basalt dated at 9.6 m.y. fills a valley directed 
down the north slope of the Coyote Flat warp and 
indicates that initial deformation to create the warp 



began before its extrusion. Howe\cr, patches of an- 
cient till that has been correlated with the Sherwin 
Till rest on the basalt but are separated from their 
source by the narrow stream-cut can\on of Coyote 
Creek, which is more than 1,000 feet deep; presumably 
much of the warping, and certainly most of the ero- 
sion resulting from w arping, post-dates the deposition 
of this till (Bateman, 1965). 

As much as 2,500 feet of displacement has taken 
place on the faults along the north and east sides of 
.McGee Mountain after the deposition of the AIcGee 
Till, which sits on a basalt 2.6 m.y. old and presum- 
ably predates the Sherwin Till. The 3.0 to 3.1 m.\-. 
andesite and quartz-latite on San Joaquin Mountain 
(Dalrymple, 1964a), at the head of the Middle Fork 
of the San Joaquin River, are cut off on the east by 
the range-front fault along the western margin of 
Long \'alley (Huber and Rinehart, 1965). The vol- 
canic rocks fill a valley through which drainage from 
.Mono Basin appears to have entered the San Joaquin 
\'alley. The McGee and San Joaquin Mountain locali- 
ties indicate that much of the range-front faulting at 
Long Valley is less than 3 miUion years old. 

The 700-thousand-\ear-old Bishop Tuff has possibly 
as much as 3,000 feet of structural relief, as mentioned 
in the section on volcanic rocks. Its upper surface has 
an altitudinal range of as much as 4,300 feet in 25 
miles, and much of this altitudinal range nia\' be due 
to deformation. At least 1,000 feet of warping of the 
tuff can be demonstrated in the vicinity of Round 
\'alley (Bateman, 1965), and the tuff is offset as much 
as 500 feet by normal faults (Putnam, 1960a). The 
fact that it was confined to a valle_\- between the Sierra 
Nevada and the White Mountains suggests that most 
of the range-front faulting predates the eruption of 
the tuff. 

According to Sharp (in Wahrhaftig and Sharp, 
1965), the Sherwin Till on benches along the west 
side of the Mono Basin predates 1,000 to 2,000 feet 
of faulting in the basin. As the Sherwin Till at the type 
locality underlies the Bishop Tuff, 1,000 to 2,000 feet 
or more of deformation must have taken place within 
the last 700 thousand )ears along the cast flank of the 
Sierra Nevada at both the north end of Ow ens \'alle\' 
and in the Mono Basin. 

In the alluvial floors of Owens \'alle\- as much as 
13 feet of net vertical displacement and 9 to 16 feet 
of right-lateral displacement took place on a fault east 
of the Alabama Hills during the Lone Pine earth- 
quake of 1870 (Bateman, 1961). 

The foregoing evidence indicates that in the south- 
ern Sierra Nevada most of the displacement along the 
eastern fault zone was accomplished within the last 
3 million years and much of it occurred within the 
last 700,000 years; much of it is therefore appreciably 
younger than an\' in the northern Sierra Nevada for 
which there is positive evidence. Most of the erosion 
in response to the late Cenozoic tilting and uplift of 



158 



Gkology of Northern California 



Bull. 190 



this southern part of the range took place more than 
3 million years ago. Thus, the faulting along the east 
side appears to be later than the tilting of the range, 
and it is probably due to the collapse of Owens \'al- 
ley, and other grabens and volcano-tectonic depres- 
sions along the crest of the broad arch defined b\' 
the Sierra Nevada on the west and the Basin Ranges 
on the east (Bateman, 1965, pi. 10). 

In summar\-, the available data on deformation on 
the west side of the southern Sierra Nevada suggest 
that deformation gradually changed southward from 
simple westward tilting in the latitude of Yosemite 
and the San Joaquin River to a fle.xure along the \\ est 
margin and vertical uplift of the east half of the 
range in the latitude of Sequoia Park and farther south. 
The amount of tilting since the early Pliocene (9.5 
m.y. ago) was about 110 feet per mile in the latitude 
of the San Joaquin and Kings Rivers, and since the 
Aliocene tilting of as much as 5" to 6!/^° took place 
along the west margin of the range near Bakersfieid. 
An average of 300 feet of erosion, concentrated in the 
canyon.s, has occurred since earl\' Pliocene time, but 
the can\ons had nearl\- their present depths 3.5 mil- 
lion >ears ago, suggesting completion of the tilting 
by then. There is little evidence of tilting in the in- 
terval between the early Eocene and the Miocene. 

Displacement along the east side northwest of Big 
Pine was accomplished through a series of en echelon 
faults alternating w ith arches and ramps, and this part 
of the front is marked b>' two large volcano-tectonic 
depressions with floors possibh' as much as 11,000 feet 



below sea level. Displacement south of Big Pine is dis- 
tributed along two parallel faults, and totals as much 
as 19,000 feet. The faults converge to a single complex 
zone at Owens Lake. Most oi the displacement along 
the eastern front has taken place in the last 3 million 
vears, and displacement has continued to the present. 
This displacement is apparently later than most of the 
tilting of the w est slofie of the range, and may there- 
fore represent collapse of the Owens V^alley graben. 

GLACIATION 

The Sierra Nevada, along with manv other high 
mountains throughout the world, was repeatedh- gla- 
ciated during the Quaternary. At the height of glaci- 
ation it bore a mountain icecap 270 miles long and 
20 to 30 mifes wide (fig. 17). During the latest glaci- 
ations, on the east side of the range valle>' glaciers 
descended from this icecap onto the bordering low- 
lands, and on the west side they extended down can- 
\()ns to altitudes of 3,000 to 4,000 feet. Some of the 
earlier glaciations were even more extensive. 

The Sierra Nevada now bears about 60 small gla- 
ciers at the heads of cirques w here the>- are protected 
from the summer sun b\- high north-facing cliffs. 
These glaciers lie at altitudes ranging from 10,600 feet 
at the north end of Yosemite Park to 11,500 to 12,000 
feet in the vicinit\' of the Palisades along the east 
boundary of Kings Canyon National Park. The peaks 
that shade them range from 11,000 feet in altitude 
at the north to 14,250 feet in altitude at the south. No 
peak in Sequoia Park, not even Mount Whitney, 




Aounloin ictcop, including pcaki 

nd clilli obova lh« firn limit, L,»0°" >>°"d on lummil olliludat o\ 

I bwl too itoop (or tnow accumulation. Ll I low»t) pook* to tiov* gl 

on Iho.r lot/th toeing iid<i. 

|Orogtopl<ic tno- limit ii 

opproilmoloir 300 400 m. 

IIOOO ISOO ll I lo»«r. 

Coniouf iniir.ol . 1000 It |305 mil 

figure 17. Wijconsin(?) glaciotion ond climofic firn limit in the Sierro Nevodo and White Mountains. From Wohrhaftig and Birmon, 1965, 
figure 2, which should be consulted for sources of information. 



1966 



Bateman and Wahrhaftig: Sikrra Nfvada 



159 




Phofo 18. Glaciated upland east of Yosemite Valley, with Half Dome in the foreground. Little Yosemite Valley extends eost behind Half Dome to 
headwaters along the west side of the Rifter Range. To the right con be seen the canyon of the Middle Fork of the San Joaquin. Mountains forming 
the central skyline are the White Mountains. U.S. Geological Survey photograph GS-OAH-3-155. 



14,500 feet high, bears an\- glaciers. The largest gla- 
cier, the Palisade Glacier at the head of Big Pine 
Creek, is about 1 mile long, but the great majority 
of them are less than !a mile long. These glaciers, 
which have formed since the climatic optimum, were 
twice their present size about 100 years ago, and have 
been shrinking ever since. Their continued existence, 
in the face of secular warming, is uncertain. 

The climatic firn limit (firn limit on south-facing 
slopes) at the time of the maximum of the last major 
glaciation is shown by contours on figure 17. As can 
be seen from this map, the orographic effect of the 
Sierra Nevada is much more pronounced than the 
poleward cooling of world climate, so that the cli- 
matic firn limit rose northeastward across the moun- 



tains. The lowest cirques, which are less than 8,000 
feet in altitude, are found on mountains in the middle 
slopes of the Sierra Nevada near Yosemite, and moun- 
tains 11,000 to 12,000 feet high east of the range bore 
no glaciers. 

At the present time no peak in the Sierra Nevada 
is above the climatic firn limit. The southernmost peak 
in the United States to have borne glaciers on its south 
slopes during historic time is Mount Shasta, 14,161 
feet in altitude. Thus, as the climatic firn limit is now 
above 14,500 feet, and probabK- above 15,000 feet, in 
the southern Sierra Nevada, the lowering of the fim 
limit to bring about the Wisconsin Glaciation was on 
the order of 3,000 feet or more. 



160 



Gkoi.ocv oi" Xorthfrn" California 



Bull. 190 




Photo 19. Yosemite Valley, froi 
□ utwosh and lake sediments, restii 



ver El Copitan looking east. The floor of the valley is underlain by 
□ n the glacier-carved bedrock floor. Photograph by Mary Hill. 



riy 2,000 feet of 



An orographic firn limit (lower limit of perennial 
snow on north-facing cirque glaciers) is difficult to 
define because of the great variation in two factors 
influencing snow retention: ( 1 ) protection from sun- 
light, and (2) accumulation bv avalanches. Thus, al- 
though it is not possible to define preciseh' the oro- 
graphic firn limit, it can be said in a general way to 
range now from about 11,700 feet at the north end 
of Yosemite Park to ll,.'iOO to l.?,000 feet in Kings 
Canyon Park. It appears that during the glacial maxi- 
mum shown in figure 17 the orographic firn limit was 
1,000 to 2,500 feet lower than the climatic firn limit, 
or at altitudes of 9,500 to 10,500 in the places where 
the glaciers are today. Southwest of Lake Tahoe, 
where the lowest glacial cirques are comparable to the 
glacier-bearing cirques in the Sierra today, the oro- 
graphic firn limit was as much as 2,500 feet lower 
than the climatic firn limit. 

The mountain icecap indicated on figure 1 7 w as 
not a continuous ice sheet above which onl\- a few 
peaks emerged, such as now e.xist on nian\- ranges of 
southern Alaska. Rather it represented the filling in 
a series of separate basins of accumulation, man\ of 



which were enclosed on three sides by an almost con- 
tinuous arete hut interconnected to the extent that ice 
flowed through some passes from one basin to an- 
other. The area of almost continuous icecap, where 
most of the dixides were submerged, included the 
basins of the Tuolumne, Stanislaus, and West Walker 
Rivers. From the Tuolumne drainage ice aLso poured 
through several pas.ses into the headwaters of the 
Merced River. 

At many places along the present drainage divide, 
glaciers from basins west of the divide spilled over the 
passes to feed ice tongues in canxons descending the 
east slope. This ice eroded broad U-shaped passes, 
which provide many of the routes of access across the 
range, such as Donner and Tioga Pass. 

The ice thickness was gcnerall>' 1,000 feet or less 
on the fianks of the aretes and in the accumulation 
basins in the headwaters of the main glaciated canxons. 
The steep glaciers on the east side of the range w ere 
also generally about 1,000 feet thick. On the west side 
of the range, ice flowing into the narrow can\-ons of 
the major rivers, such as the Tuolumne, Merced, San 
Joaquin, and Kings, filled them to great depths. During 



1966 



BaTK.MAN and W'aHRU AKIK.: Sll KRA NkVADA 



161 



the last glaciation, the Tuolumne Glacier was 4,000 
feet thick in the Grand Canvon of the Tuolumne, 
where it spilled over the south rim of the canyon. 
During an earlier glaciation, the Merced Glacier must 
have had a maximum thickness of nearly 6,000 feet in 
Yosemitc \'alley (see fig. 14, photo 19), including 
2,000 feet excavated by the ice below the valle>"s bed- 
rock lip (Gutenberg and others, 1956; Matthes, 1930). 

The amount of erosion that the glaciers could ac- 
complish was chiefly controlled by the jointing and 
weathering of the granitic rocks that floor most of 
the glaciated areas. Headwater basins were opened to 
broad cirques; lake basins were can'ed throughout 
the glaciated region; and at the glacial termini were 
formed deep basins, such as hold Donner Lake, Fallen 
Leaf Lake, and Emerald Ba\', and the alluvium-filled 
rock basin 2,000 feet deep beneath the floor of Yosem- 
ite \"alley. Alany of the valleys were given U-shaped 
cross-profiles, and a number were deepened consider- 
ably. Weathered bedrock was removed from most of 
the glaciated areas, and trenches were etched along 
the joints, giving man\' cirque and basin floors a bil- 
lowy topography. Frost action sharpened the ridges 
and peaks to precipitous aretes and horns. Much of 
the unusual beauty of the High Sierra is the result of 
this glacial modification of a previously dissected land- 
scape. 

In spite of these spectacular examples of glacial 
erosion, it is remarkable also what the glaciers did not 
do. Broad benches that predate glaciation, such as the 
Chagoopa Plateau and other benches along the Kern 
River Canyon and the benches along the South Fork 
of the San Joaquin, were little modified by the ice 
that poured over them. Many gorges retained a 
\^-shaped profile, in spite of the vigor of the glaciers 
that poured through them. Examples are the Grand 
Canyon of the Tuolumne, the canyon of the iMerced 
below Yosemite, and the canyon of the South Fork 
of the San Joaquin between Mono Hot Springs and 
Balloon Dome. The \^-shaped profiles of these canyons 
may have been preserved by the presence of large- 
scale sheeting parallel to the original canyon walls, 
which controlled the pattern of glacial erosion. 

Material eroded by the glaciers was either deposited 
in the form of moraines or delivered to meltwater 
streams to be carried out of the glaciated area. The 
most impressive moraines are at the mouths of canyons 
along the east side of the Sierra. These moraines pro- 
ject 1 to 3 miles directly away from the mountain 
front on either side of the glaciated canyons, parallel 
to the direction of glacier flow, indicating that the 
glaciers did not spread as piedmont lobes but main- 
tained the widths they had in their mountain canyons 
by building walls for themselves in the form of sharp- 
crested embankments a few hundred to a thousand 
feet high. Many of these morainal ridges have double 
or triple crests, with narrow trenches running the 
length of the ridge betsveen the crests, indicating two 
or three advances of the ice during their construction. 



On the forested west slope of tiie Sierra the moraines 
are lower and less conspicuous, and are commonly 
difficult to recognize. They reach their most impres- 
sive size along the walls of the broad upper valley of 
the South Fork of the San Joaquin River (Birman, 
1964), north of Kaiser Crest, and along Roaring River, 
tributary of the South Fork of the Kings. Low ter- 
minal moraines cross the floor of ^'osemite \''alley near 
Bridalveil Fall. 

The bulk of the glacial debris on the west side was 
probably transported into the Great Valley by swift 
meltwater streams. Within the range the canyons are 
so steep and narrow that outwash terraces have not 
been preserved. Roadcuts in some of the canyons, such 
as those in Merced Cannon between Briceburg and 
El Portal, have exposed patches of outwash of several 
ages and degrees of weathering, preserved beneath 
mantles of colluvium. 

The lithology of the alluvium from the major 
rivers on the east side of the Great Valle>' indicates 
its glacial origin (Janda, 1965b). It contains numerous 
boulders and pebbles of fresh granitic rocks, rock types 
that are rare in alluvium from unglaciated basins or in 
preglacial alluvium. It also contains layers of finely 
laminated silt and fine sand consisting of unweathered 
fragments of hornblende, augite, biotite, feldspar, and 
quartz. Silt of such mineralog\- could not have been 
produced b\- ordinary weathering processes and must 
have originated as glacial rock flour. 

That the Sierra Nevada was glaciated more than 
once during the Quaternar\- was recognized in the 
late 19th century (Russell, 1889; Turner, 1900; W. D. 
Johnston, unpublished notes). The classic works on 
multiple glaciation in the Sierra Nevada are those of 
Matthes (1930), who established three glacial stages 
on the west side of the Sierra Nevada around Yosemite 
\'alley, and of Blackwelder (1931), who established 
four glacial stages on the east side. Blackwelder's ter- 
minology of Tioga, Tahoe, Sherwin, and McGee, from 
youngest to oldest, has been adopted wherever corre- 
lations with his type localities w ere possible. Sharp and 
Birman (1963) have added t\vo new Pleistocene gla- 
ciations to the chronology of Blackwelder: the Te- 
na\a, between the Tioga and the Tahoe; and the Mono 
Basin, between the Tahoe and the Sherwin. Birman 
(1964) has, in addition, named three post-Tahoe gla- 
ciations, two of which, at least, are post-altithermal. 

The difficulty of correlating glaciations along the 
length of the range has persuaded Birkeland ( 1964) 
to adopt local names for the pre-Tahoe glaciations 
north of Lake Tahoe. Correlation across the range also 
presents great difl^culties; Matthes and Blackwelder, 
although the>- were familiar with each other's work, 
were unable to come up with a mutually satisfactor\- 
correlation. Birman (1964), by tracing glacial deposits 
and landforms across the range between the South 
Fork of the San Joaquin and Rock Creek, and by sta- 
tistical study of Ijoulder-w eathering ratios, has made a 
correlation of the younger glaciations across the range, 



162 



Gfoi.ogy of Northern California 



Bull. 190 




Photo 20. Roaring River valley in Kings Conyon National Pork, seen from the west over Sugorloof Meadow. In the background ore the serrated 
horns and aretes of the Great Western and Kings-Kern Divides. The prominent morainol ridges that enclose the valley ore probably of Tohoe and 
Tioga oge. U.S. Geological Survey photograph GS-OAL-l-2n. 



although he could distinguish onl\- one pre-Tahoe 
glaciation on the west side. 

Some of the glacial deposits are overlain or under- 
lain b\- radionietricalK- dated volcanic deposits (Dal- 
ryniple, 1964a; 1964b; DnlrvmnlF Co.\ and Doell, 
196.')); hence, an absolute chronology of some of the 
glaciations can be approximated. At the moment of 
writing, the .McGee and Sherwin deposits are the old- 
est Quaternary glacial deposits in the world associated 
with radiometrically dated rocks. 

Tectonics and erosion have considerably obscured 
the glacial record. Consequently one major concern 
has been the possibility- that there are additional, un- 
recognized, glaciations, the critical evidence for which 
is missing through erosion or burial. A more complete 
record of glaciation is likely to be preserved in the 
alluvium of the Great \\illey than in the mountains 
themselves. Three and possibly four separate alluvial 
units of glacial origin, separated by erosional uncon- 
formities with well-developed soils, have been recog- 
nized along the east side of the vallev (Davis and 
Hall, 1959; Arkley, 1962; Janda, 1965b). Janda has 
correlated these with glacial deposits in the High 
Sierra. 



The glacial deposits and coeval alluvial deposits can 
be divided into five groups on the basis of age and 
degree of preservation; from youngest to oldest these 
are: 

( 1 ) Extremel\- fresh bouldery moraines deposited 
by glaciers that advanced only a short distance from 
the cirque heads. Included arc the Matthcs and Recess 
Peak Glaciations of Birnian (1964) and neoglacial de- 
posits recognized by Birkeland ( 1964). These are post- 
aititiiermal in age. 

(2) Somewhat more extensive and more weathered 
rills, intermediate in character between the Tioga Tills 
and the group described above. Included arc tiic de- 
posits of Hilgard Glaciation of Birman ( 1964) and the 
Frog Lake Till of Birkeland (1964). These glacial 
deposits may result from cither the latest pulse of the 
Wisconsin or an early Recent (post-altithcrmal) ad- 
vance. 

(3) Well-preserved moraines marking a sequence of 
glaciations, all of which were about as extensive as 
shown on figure 17. None of the moraines shows an\ 
development of a textural B horizon in the soil (Birke- 
land, 1964). This group includes moraines of the 



1966 



Batf.man and Wahrhaftig: Sierra Nevada 



163 



Tioga, Tenaya, Tahoe, and possibly the Mono Basin 
Glaciations. Tioga and Tahoe are recognized through- 
out the length of the glaciated Sierra Nevada. Tenaya 
and iMono Basin have been recognized in only a few 
localities south of Sonora Pass. In the walls of excava- 
tions, such as roadcuts, the Tioga can be distinguished 
from the Tahoe, because boulders in the Tioga Till 
are fresh throughout, whereas many of the granodio- 
rite and quartz-monzonite boulders beneath the sur- 
face to depths of 5 to 10 feet in the Tahoe deposits are 
altered to gruss (Birkeland, 1964; Wahrhaftig, 1965a, 
1965e). No roadcut exposures of the Tenaya or Mono 
Basin Tills are available. In the absence of cuts, distinc- 
tion and correlation of moraines of this sequence are 
based on depth of erosion of axial stream channels, 
sharpness and degree of preservation of the moraines 
(Blackwelder, 1931), and boulder-weathering ratios 
and abundance of fine materials in the surface soil 
(Sharp and Birman, 1963;Birman, 1964; Sharp, 1965a,b; 
Sharp hi Wahrhaftig and Sharp, 1965). 

The moraines c'^ this group are bracketed by a 
radiocarbon age of 9,800 ± 800 years (David P. 
Adam, written communication, 1965) for Tioga Till 
near Echo Summit; and by potassium-argon dates of 
90,000 ± 90,000 and 60,000 ± 50,000 years on basalt 
beneath Tahoe Till at Sawmill Canyon ( Dairy mple, 
1964b). Hence the sequence Tioga-Tenaya-Tahoe 
corresponds to the Wisconsin in the broad sense of 
midwest chronology. Through study of ice-dammed 
flood deposits from Lake Tahoe, Birkeland (1965a) 
has correlated the Tahoe and Tioga with the Eetza 
and Seehoo Formations, respectively, of Lake Lahon- 
tan (Morrison, 1964). 

The Modesto Formation of Davis and Hall (1959) 
in the Eastern San Joaquin \'alley has been correlated 
by Janda (1965b) ^\•ith the sequence Tioga-Tahoe- 
Tenaya, on the basis of the lack of a textural B hori- 
zon in its soil. According to Janda the formation has 
three terraces with slightly different weak soil de- 
velopment; these mav correlate with the three glaci- 
ations recognized by Birman at the head of the San 
Joaquin drainage. 

(4) Poorly preserved moraines and well-preserved 
outwash terraces, upon which there is a soil with a 
well-developed B horizon. Till and outwash of the 
Donner Lake Glaciation (Birkeland, 1964) in the 
Truckee area is assigned to this group. The glaciation 
post-dates deformation in the Truckee area. The 
Riverbank Formation of Davis and Hall (1959) in the 
eastern San Joaquin Valley, which is slightly dissected 
and has a well-developed soil with an oxidized clay- 
rich B horizon or a silica hardpan, or both, is also as- 
signed to this group. With the exception of the deposits 
of the Truckee area, no extensive glacial deposits have 
been assigned to this period of glaciation. The e.xcel- 
lent soil development indicates that it is much older 
than Wisconsin. A deposit of weathered gravel, which 
occurs above the limit of the Tahoe Glaciation just 
west of Mammoth Mountain, contains quartz-latite 



derived from Mammoth Mountain, wliich has been 
dated at 370,000 years (Janda, 1965a; for discussion of 
date, see Dalrymple, 1964). If this deposit is a till and 
is to be correlated with the Donner Lake Glaciation, 
it is probably younger than 370,000 years and older 
than the Tahoe Glaciation. 

( 5 ) Deposits of till, \vithout morainal topography, 
buried beneath volcanic deposits, or perched on moun- 
taintops and benches several thousand feet above pres- 
ent-day glaciated can\on floors. The till of this group 
has customarily- been assigned to two glaciations, the 
Sherwin and the McGee (Blackwelder, 1930; Putnam, 
1960a, 1960b, 1962; Rinehart and Ross, 1957, 1964). 
The type locality of the Sherwin Till is on the Sher- 
w in Grade of U.S. Highway 395, where it is overlain 
b>- the Bishop TuflF, dated at 700,000 years (Dal- 
r\mple. Cox, and Doell, 1965; Putnam, 1960a; Rine- 
hart and Ross, 1957; Sharp, 1965b). It therefore pre- 
dates the 1,000-3,000 feet of deformation that aff^ected 
the Bishop Tuff^. The till is deeply weathered and 
lacks morainal topography. Judging from the even 
character of the till surface buried beneath the Bishop 
Tuff', its morainal topography was obliterated before 
the deposition of the tuff^. It may, therefore, be consid- 
erably older than the tuff^. 

Farther north, deposits of till on intercanyon 
benches on the west side of the Mono Basin are cor- 
related by Sharp (i?! Wahrhaftig and Sharp, 1965) 
with the Sherwin Glaciation. According to Sharp, 
these were deposited before the collapse of the Mono 
Basin, and therefore predate several thousand feet of 
displacement on the faults enclosing that basin, and 
according to Pakiser, Press, and Kane (1960), they 
may predate as much as 18,000 feet of displacement. 

The McGee Till rests on a 10,500-foot plateau on 
the summit of McGee Mountain, about 2,000 feet 
above the floor of McGee Creek canyon to the south, 
and more than 3,000 feet above the floor of Long 
\'alley. The most abundant boulders in the till come 
from granodiorite exposed at the head of McGee 
Creek, a half-dozen miles to the south. The til! rests 
on basalt with a potassium-argon age of 2.6 m.y. (Dal- 
rymple, 1963). Blackwelder (1931), Putnam' (1960, 
1962) and Rinehart and Ross (1964) concluded that 
the till was deposited before several thousand feet of 
displacement on the range-front faults on the north 
and east sides of McGee Mountain, and when McGee 
Creek canyon was much shallower than today. Love- 
joy (1964) argued that the till \\as deposited by a 
glacier when the topography was essentially as it is 
today. Christensen (1966) has reviewed the evi- 
dence, and presented a justification for the views of 
Black\\elder, Putnam, and Rinehart and Ross. 

Because the Sherwin Till is found at the base of 
fault scarps like those bordering McGee Mountain, 
Blackwelder (1931) and all subsequent workers have 
concluded that the Sherwin and McGee are separate 
glaciations, and that several thousand feet of displace- 
ment occurred on the range-front fault in the interval 



164 



ClOI.OGV OK N'ORTHF.RN Caijkorma 



Bull. 190 




Photo 21. The northeast foce of the Sierra Nevada in Mount Morrison quadrangle as seen from hills eost of Deadman Summit. Mount Morrison 
is the sharp peak on skyline on the right. The broad flat mountain, on the left, slightly in shadow and in front of snowclad peaks, is McGee 
Mountain. Deposits of the McGee Till mantle its flat summit, and directly below it is the complex of moraines of the Convict Greek glacier. The plain 
below the moraines is the floor of Long Valley. The hills from which the photograph was token ore part of the volcanic sequence erupted on the 
floor of the Long Valley volcano-tectonic depression, and the mountain front here is one woll of that depression. Photograph by John Burnett. 



between them. .-Mtliough this is probably so, one can- 
not reall\- prove that the Sherwin and the McGee are 
separate glaciations. 

In the Truckee area in the northern part of the 
range, scattered remnants of till and out\\ash older 
than the Donner Lake Glaciation are assigned to a 
glaciation named by Birkeland ( 1964) the Hohart 
Glaciation. As the till occurs at the present river level 
on the Truckee River, the glaciation presumabl\' oc- 
curred after the river eroded through the volcanic 
rocks of the Lousetown Formation to its present posi- 
tion. .'Vnd because the youngest Lousetown volcanics 
involved are 1.2 million \ears old, the Hobart Glaci- 
ation took place less than 1.2 million \ears ago, prob- 
abl\- much less. The Hobart may correlate with the 
Sherwin, but such a correlation cannot be proved. 

Alluvium in the San Joaquin Valley that is probably 
outwash from glaciations that may correlate with the 
Sherwin or McGee or both, makes up the Turlock 
Lake Formation of Davis and Hall (1959; see Janda, 
1965b). In the Friant area, where the San Joaquin 
River debouches onto the alluvial plain, this forma- 



tion consists of two units separated by an erosional 
unconformity and a well-developed soil. At the base 
of tlie upper unit is a pumiceous ash, on which a date 
of 600,000 years has been obtained (Janda, 1965b). 
The upper unit of the Turlock Lake Formation is in- 
tricatel>' dissected with a relief of about 100 to 200 
feet, and on this surface of dissection is a soil with a 
well-developed te.xtural B horizon. Of the two glaci- 
ations represented by the Turlock Lake, one is slightly 
\-ounger than 600,000 years, and the other much older. 
The chronology of glaciations described in the para- 
graphs abo\c is summarized in table 2. 

SUMMARY OF GEOLOGIC HISTORY 

During the Paleozoic the Sierra Nevada region was 
beneath the sea receiving sediments in the east and 
volcanic and associated sedimentary deposits in the 
west. Doubtless the Mi.ssissippian .-Xntler orogen>' of 
Nevada affected the Sierra Nevada region, and other 
disturbance may also have occurred during the Paleo- 
zoic. In Late Permian or Triassic time a north- to 
north\vest-trending synclinal trough began to subside 



1966 



BaTKMAN and VVahRHAI' IK.: SlI.RKA NlA'ADA 
TABLE 2. Provisional correlation of glacial and alluvial deposits in the Sierra Nevada. 



165 



Age 



Mid-continent 
glaciations 



Wisconsin 
Glaciation 



Correlation 

with 

mid-continent 
glaciations 
uncertain 



Lake Lahontan 
(Morrison, 
1961, 1964) 



Fallon 
Formation 



Tahoe area 
(Birkeland, 1964) 



Neoglaciation 



Southern Sierra Nevada 
(Blackwelder, 1931; Sharp and 
Birman, 1963, Birman, 1964) 



Matthes Till 
Recess Peak 'I'i 



Sehoo 

Formation 



Eetza 

Formation 



? Frog Lake Till ? Hilgard Till 
9,S00y.' 



Two pre-Lake 
Lahontan units 
(Morrison, 
1965) 



Tioga Till 



Tioga Till 

Tenaya Till 

Tahoe Till 



-(60,000-90,000y.*)- 



r Mono Basin Till 



Donner Lake 
Till 



Till(?) on Mammoth Mountain 
(Janda, 1965a) 

(370,OOOy.*) 



1.2 m.y. (under 
Hobart) 



Glaciation between tuff of Reds 
? Meadow and andesite of 
Devils Postpile (Huber, 
oral comm., 1965) 

(Bishop Tuff, 700,000y.') 



Sherwin Till 
McGee Till 
2.5 m.y. (under McGee) 



Alluvial formations of the 

San Joaquin Valley 

(Davis and Hall, 1959; Arkley, 

1962; Janda, 196S-b) 



Modesto Formation 



Riverbank Formation 



Turlock Lake Formation 
(upper unit) 



600,000y.* 



.' Turlock Lake Formation 
(lower unit) 



of radiometric dates, see text. 

in the area of the Sierra Nevada. This trough was filled 
during the Late Triassic and Jurassic with great thici<- 
nesses of volcanogenic materials. Repeated disturb- 
ances are indicated b)' unconformities and hv super- 
imposed minor fold systems. Steep beds, cleavages, 
and lineations require that the synclinal structure ex- 
tended downward many miles below the present level 
of exposure. Faults with stratigraphic separations of 
many miles cut the west limb of the synclinorium, and 
serpentine along these faults suggests that the\' pene- 
trated into the mantle. 

Magma of granitic composition was generated in 
the lower part of this synclinorium during at least 
three widely separated times — the Late Triassic or 
Early Jurassic, the Late Jurassic, and early Late Cre- 
taceous — and possibly at other times as well. The gen- 
eration of magma probably was caused in part b\' the 
depression of sialic rocks in the keel of the synclinor- 
ium into deep zones of high temperature and in part 
by thickening of the sial, which contains a greater 
abundance of the heat-producing radioactive elements 



than the underlying more femic earth zones. Addi- 
tional heat might have been supplied by convective 
overturn in the mantle or by the intrusion of dike 
swarms into the base of the crust, but no evidence 
can be cited in support of either process. 

Granitic magma is significantly less dense than gra- 
nitic rock of the same composition and consequenth' 
much of it worked its wa\- upw ard, in much the same 
manner as salt domes, into the overlying rock. The 
rising magmas exploited faults and other lines of struc- 
tural weakness, and crowded the country rocks aside. 
Most of the magmas rose into the axial region of the 
synclinorium, but some worked upward along its 
limbs. As the magmas rose, reactions took place be- 
tween them and the country rocks, especially between 
felsic magmas and amphibolitic wall rock. Although 
convincing evidence of the melting of wall and roof 
rocks by heat given off by magmas has not been ob- 
served, some of the less refractor\' countr\' rocks, such 
as shale or graywacke, probably were incorporated 
in magmas by melting. Differentiation, chiefly through 



166 



Geology of Northkrn Cai.ikorma 



Bull. 190 



fractional crystallization, took place \\ithin the magmas 
as the\- rose and produced a diversity of compositions 
in the rising magmas and in the granitic rocks. In gen- 
eral, the most highly differentiated and most felsic 
magmas penetrated highest, causing the average com- 
position of the granitic rocks to be more felsic upward. 
As a consequence of the upw ard movement and differ- 
entiation of magmas, the batholith is composed of a 
mosaic of plutons of different composition and texture, 
\\ hich are either in sharp contact with one another or 
are separated from one another by thin septa of meta- 
morphic or older granitic rocks. 

The depression of the svnclinorium doubtless dis- 
turbed the isostatic equilibrium, which required uplift 
for adjustment. Because of erosion the re-establishment 
of isostatic equilibrium was a long process that may 
still be going on today. Considerations of the volume 
of epiclastic material that was deposited in basins ad- 
jacent to a broad north-trending highland that in- 
cluded the Sierra Nevada, and of the significance of 
andalusite and sillimanite in contact-metamorphic min- 
eral assemblages suggest that at least 9 miles of rock 
was eroded from the Sierra Nevada since the two 
earlier periods of piutonism in Late Triassic or Earl)' 
Jurassic and Late Jurassic time. 

This great amount of erosion was probably com- 
pleted along the west margin of the Sierra Nevada by 
Coniacian time (about 85 m.y. ago in the Geol. Soc. 
London time scale, 1964), when the last major granitic 
plutons were emplaced, and was certainly completed 
for much of the Sierra Nevada by the end of earl\- 
Eocene time (about 55 m.y. ago). Consequently be- 
tween 9 and 17 miles of cover was eroded from the 
western Sierra Nevada in a time interval of between 
55 and 80 m.y., indicating the area was stripped at a 
rate of Vi to 1 Vz feet per thousand years. 

The timespan from early Eocene to late Oligo- 
cene (about 25 to 30 m.y.) was one of virtual stand- 
still in the Sierra. The bulk of the erosion had been 
completed; river channels whose ages (based on both 
fossils and radiometric dates) range over this interval 
are nearly parallel and at the same altitude. Even 
channels as young as early Pliocene in age show ver\' 
little difference in slope and altitude from channels of 
early Eocene age. During the Eocene the Sierra may 
have been about 3,000 to 5,000 feet high near its crest; 
along its western margin were mountains of resistant 
greenstone 1,500 to 2,000 feet high. The still-preserved 
channel segments are filled with quartz-rich gravels 
which are 500 feet thick in places and from which 
man\- millions of dollars worth of gold was obtained. 
."Mong the west margin of the range, the gravels grade 
into littoral and marine sands and clays of the lone 
Formation. The warm-temperate to tropical climate 
of the early Cenozoic favored deposition of quartz- 
anau.xite sands and halloysitic clays in the lone For- 
mation, where they rest on lithomargic and lateritic 
soils. The bulk of the auriferous gravels also date from 
this interval, although some of the high-level gold- 



bearing channel gravels (the intervolcanic gravels) are 
as young as Pliocene. 

A period of volcanic activity began in the central 
Sierra Nevada in middle Oligocene time (about 30 to 
33 ni.v. ago) with the eruption of predominantly 
rh\()litic tuffs and ash flows (the X'alley Springs For- 
niation). Rh\olitic eruptions lasted until late Mio- 
cene time (about 20 m.y. ago) and were followed by 
eruptions of andesitic mudflow s which lasted from late 
.Miocene to late Pliocene time (late Hemphillian — 
about 5 m.y. ago). The total thickness of the rh\olitic 
rocks is in few places more than 400 feet, but the 
andesitic rocks arc much thicker and range from a 
maximum of 3,000 feet along the crest of the range to 
about 500 feet in the San Joaquin V'alley west of the 
Sierra Nevada. The volcanic rocks are intercalated 
with gravels, man\- of which were mined for their 
gold content. Only locall\' can more than 30 to 40 
flows be observed in a single section a few thousand 
feet thick, and commonly fewer flows are present. 
Thus as far as the existing record tells us, volcanic 
eruptions probably occurred in any one place only a 
few times every million \ears. The lavas, tuffs, and 
mudflows do not suggest an environment an\' more 
catacl>smic, on the average, than that prevailing in the 
Cascade Range today. 

The volcanic cover was extensive only north of the 
Tuolumne River, and even in that region not all of the 
Sierra Nevada was buried. Groups of granitic moun- 
tains near the range crest, such as those around 
Pyramid Peak, appear to have risen above the volcanic 
mudflow surface; and along the west front of the 
range northwest-trending ridges one to two thousand 
feet high, upheld by resistant greenstone, almost cer- 
tainly rose above the volcanic plain. 

South of the Tuolumne River the Tertiary events in 
the Sierra Nevada are represented chiefl\' by scattered 
volcanic deposits, mainly basaltic flows, whose ages 
seem to cluster around 9.5 and 2 to 4 m.y. (Dalrymple, 
1963), and by the erosion surfaces developed on the 
volcanic and granitic rocks. The granitic rocks that 
underlie the bulk of the southern part of the range 
were subjected to weathering and erosion throughout 
the Cenozoic, and have evolved a distinctive "stepped" 
topograph)- that ma\- be peculiar to biotite-bearing 
crystalline rocks. 

At some time in the Pliocene, possibl\- in middle or 
late Pliocene time, the northern Sierra Nevada — and 
probably the southern Sierra Nevada as well — was 
strongl)- uplifted and tilted to the west. That uplift 
of the southern Sierra Nevada began before this in 
carl\ Miocene time is suggested by evidence in the 
sedimentar\- deposits of the San Joaquin \'alley. In 
response to the major uplift, the rivers on the west 
slope incised their canyons to depths of 2,000 to 4,000 
feet below the ba.se of the Tertiar\- channels, whose 
remnants are preserved on the flat-topped interstream 
ridges in the northern part of the range. Basalt flows 
dated at 3.3 m.y. in the Kern River canyon arc evi- 



1966 



Bateman and VVahrhaftk;: Sierra Nevada 



167 



^^^^^B^^^ 






1 '«,».- 


»^^a»^5^|M^^^^^^^^B 


^^ 






bmhi^^^^^^^^^^hbKh^^^ 




1 


—--*-- ' 


^^^^^""■yTBB^^^^^B^^^g^^^;^ 


i&~ 


s 


♦'*^i^r^ 


> .'::>s^?«cS'-#^^^^ 




Blh(>IWIig>^" 










■ ..> 1.- ■ 




• ■■■"* • ■■'■■■ '•• ■'S^'^-rf'-Y^'^h-w 

''r' ' '. . -,••■ .ii^>" ■''■'' •'■■■■', .•.•»v *.-''■ 




% ' 





Photo 22. West-facing step fronts and flat to east-sloping plate 
Fresno County toward the west half of Sequoia Park. Tenmile Cre 
drains eastward from Big Meadow {the irregular white patch in 
on extreme left, iust behind Big Meadow Creek, marked by a l< 



ous of the southern Sierra Nevada, a 
sk is in lower right foreground. In th 
the forest-covered plateau in the 
iw cliff along the top of its near foc^ 



^en looking south from over Hume Lake in 

iddle distance on left. Big Meadow Creek 

ddle distance). The white dome-like mountain 

s Shell Mountain. The Generals Highwoy 



follows the ridge that extends diagonally across the picture from the head of Tenmile Creek toward Shell /Aountain. The canyon beyond this ridge 
on the extreme right is Redwood Canyon. High sharp-crested asymmetric ridge left of Redwood Canyon, with bold-rock outcrops on its right side, is 
Big Boldy Ridge. Rising out of the mist behind Big Boldy Ridge are the Ash Peaks in Sequoia Park. High peaks on the skyline on extreme left ore 
Vandever Mountain and White Chief Peak, south of Mineral King. 

The characteristics of the stepped topography ore particularly well exemplified by the high east-sloping plateau enclosing Big Meadow, with its 
westward-foci ng escarpment. U.S. Geological Survey photograph GS-OAL-1-22. 



dence that there the bulk of the downcutting was 
completed before the end of Pliocene time. Elsewhere 
most of the canyon cutting appears to have preceded 
the earliest recognizable glaciation on the west slope. 
During the Pliocene, also, the eastern boundary 
fault system of the Sierra Nevada was active. This 
activity appears to have begun about 10 m.y. ago or 
perhaps a little later. In the northern part of the Sierra 
Nevada, most of the faulting appears to have been 



completed by 2 million years ago, but in the southern 
part of the range much of it took place later. Thus 
faulting along the east side of the Sierra Nevada prob- 
ably lagged behind the westward tilting of the range. 
In the Owens Valley segment, at least, the main fault- 
ing appears to be much later and ma\' represent col- 
lapse of the 0\\ens Valley block. The magnitude of 
the faulting and uplift are likewise not the same. Up- 
lift in the San Joaquin segments of the Sierra Nevada 



16H 



GKOl.Oin OK N'OKIIIKKN C>.\I.I lOKMA 



Bull. 190 




Photo 23. The rugged glaciated country of the High Sierra seen looking south toward the Kings-Kern Divide from over Gardiner Basin in Kings 
Canyon Notional Park. Mount Gardiner is near the lower right corner, and in the center foreground a rock glacier about 'i mile long extends from 
the base of its eost ridge. Charlotte Lake, east base of Mount Bogo, is at the east (left) end of the valley directly behind Mount Gardiner Ridge. 
Deep canyon hidden by Mount Bogo is Bubbs Creek canyon, and the lake-dotted canyon directly behind Mount Bago is East Creek canyon, heading 
in Harrison Pass. Deep canyon in distance beyond Harrison Poss is Kern Conyon. The high peoks on the right are port of the Great Western Divide; 
those on the left mark the crest of the Sierra Nevada. High asymmetric peak at extreme left is Mount Whitney. The flat mountain tops ond plateaus 
that step downward from Mount Whitney to the Kern Canyon were considered by Motthes to be remnants of the Cirque Peak, Boreol, ond Chagoopo 
surfaces. U.S. Geological Survey Photograph GS-OAL-1-43. 



during Pliocene and Plei.stocene time probably 
amounted to no more than 6,000 feet — in the Lake 
Tahoe region it is onl\' about 4,000 feet. Yet the relief 
on the basement surface from the range crest to the 
base of the alluvium in Owens Vallev is 14,000 to 
19,000 feet. 

The Sierra Nevada, in common with all other 
alpine and arctic regions, was glaciated several times 
during the Pleistocene. The two earliest glaciations, 
the Sherwin and McGee, are between 2.5 and 0.7 mil- 
lion years old and are the oldest glaciations strati- 



graphicalh- related to radiometrically dated materials 
in the world. Four to six glaciations have been recog- 
nized on the east side of the Sierra Nevada, the last 
two or three corresponding to the Wisconsin; on the 
west side of the Sierra direct evidence indicates only 
four glaciations, but indirect evidence in the San Joa- 
quin \''alle\' indicates four major glacial periods, of 
which the Wisconsin — comprising three glaciations — 
is the last. .Moraines of the two oldest glaciations of 
the east side, the Sherwin and McGee, have lost their 
topographic form. These older glaciations seem to 



1966 



Batf.man and Wahrhaktig: Sii rra Nivada 



169 



have taken place before much of the faulting along 
the east side of the range, whereas the well-preserved 
moraines of the younger glaciations (Mono Basin, 
Tahoe, Tenaya, and Tioga) extend from the existing 
canyon mouths onto the basin floors. The Wisconsin 
firn limits were 6,500 to 8,000 feet above sea level in 
the northern Sierra Nevada and 10,500 to 12,000 feet 
high in the southern Sierra Nevada, or about 2,500 to 



3,000 feet lower than at present. The crest of the range 
w as covered by a mountain icecap which sent tongues 
10 to 40 miles long down the can>ons on the west side. 
The glaciation came to an end about 9,500 years ago, 
and the postglacial climate has been marked by a 
period of relative warmth, followed by a period in the 
last 2,000 to 3,000 years during which the climate 
cooled enough to form small cirque glaciers. 



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mantle, western United States: Science, v. 146, no. 3651, p. 1539- 

1549. 
1964, Crustol structure from Pocific Basin to central Nevada: Jour. 

Geophys. Research, v. 69, no. 22, p. 4813-4837. 

Thompson, G. A., ond White, D. E., 1964, Regional geology of the 
Steamboat Springs oreo, Washoe County, Nevada: U.S. Geol. Survey 
Prof. Paper 458-A, 52 p. 

Trask, J. B., (1854|, Report on the geology of the coast mountains, 
and port of the Sierra Nevoda-embrocing their industrial resources 
in agriculture and mining: California Geol. Survey, Senate Doc. 9, 
Sess. 1854, p. 1-88. 



Turner, H. W., 1894, Description of the Jackson quadrangle, California: 

U.S. Geol. Survey Geol. Atlas, Folio 11, [6) p. 
1900, The Pleistocene geology of the south central Sierra Nevada 

with especiol reference to the origin of Yosemite Volley: California 

Acad. Sci. Proc, 3d ser.. Geology, v. 1, no. 9, p. 262-321. 
Turner, H. W., and Ronsome, F. L., 1898, Big Trees, Colifornia: U.S. 

Geol. Survey Geol. Atlas, Folio 51, [8) p. 
Tuttle, O. F., and Bowen, N. L., 1958, Origin of granite in the light of 

experimental studies in the system NoAlSi.O-KAISiO-SiO^-HiO: Geol. 

Soc. America Mem. 74, 153 p. 
U.S. Geological Survey, 1964, Geological Survey Reseorch 1964: U.S. 

Geol. Survey Prof. Paper 501 -A, 375 p. 
VanderHoof, V. L., 1933, A skull of Phi'ohippus lonlalus from the later 

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Dept. Geol. Sci. Bull., v. 23, no. 5, p. 183-194. 
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Geod. Comm., Gravity Expeditions at Sea, 1923-1932, v. 2, 208 | 
Wohrhoftig, Clyde, 1962, Geomorphology of the Yosemite Valley regioi 

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1965a, Convict Lake to Rock Creek, in Guidebook for Field Con 

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of the Puget group. King County, Washington: U.S. Geol. Survey 

Prof. Poper 424-C, p. C230-C232. 
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heat in Sierra Nevada plutons: Jour. Geophys. Research, v. 69, no. 

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Museum of Comparative Zoology: Harvard Coll. Mus. Comp. Zoology 

Bull., V. 123, no. 3, p. 85-110. 



GEOLOGY OF THE TAYLORSVILLE AREA, 
NORTHERN SIERRA NEVADA 

By Vernon E. McMath 
Continental Oil Co., Ponca City, Oklahoma 



In the northeastern Sierra Nevada, the great batho- 
lithic edifice of the High Sierra ignominioush* loses 
its footing amidst terrain dominated by volcanic geo- 
s\nciinai fill. The eastern marginal fault s\steni of the 
High Sierra gives way to a series of lesser Basin and 
Range structures. The degree of metamorphism be- 
comes less. But it is these very diminutions, especiallv 
the paucity of plutons, that account for the signifi- 
cance of this relativeh- small area in the northernmost 
Sierra Nevada; the geos\nclinal record has not been 
obliterated. The significance of this record was dem- 
onstrated by J. S. Diller in a series of papers culminat- 
ing in U.S. Geological Survev Bull. 353, Geology of 
the Taylorsville Region ( 1908).^his region, discussed 
herein, is bounded on the south by the 40th parallel 
(fig. 1), but much of the Paleozoic section continues 
beyond the parallel, southward into the adjacent 
Downieville 30-minute quadrangle (Turner, 1897)7\ 

Regionally but lightly metamorphosed Paleozoic, 
Triassic, and Jurassic marine rocks, all deformed in 
the Nevadan orogeny, underlie most of the Taylors- 
ville area. The younger granitic plutons and still 
younger Tertiary volcanic rocks, though locally prom- 
inent, are excluded from further consideration here. 
Because the older stratified rocks are metamorphosed, 
the prefix "meta" should be attached to the names of 
all types except those intrinsically connotating meta- 
morphism. For the sake of simplicity, however, the 
prefix is omitted but is understood to apply to all the 
pre-Nevadan rocks discussed here. 

[Regional metamorphism is of the greenschist facies] 
although locally a prehnite-albite assemblage suggests 
the lower grade prehnite-pumpellyite metagray\\acke 
facies (Coombs, 1960, 1961). JVIetamorphic foliation 
ranges from well developed in phyllites to impercep- 
tible in lava floA\s, sills, and some tuffs and pyroclastic 
breccias. It is generally an axial plane cleavage and is 
more consistent in attitude than bedding. Locally, bed- 
ding has been overturned beyond the position of the 
axial plane so that bedding-cleavage relations indicate 
an incorrect direction of top. 0\\ing to penetrative 
deformation, the degree of elongation of originall\- 
equidiniensional fabric elements may be as much as 
three- or four-fold but is generally much less. Where 
original elements have been elongated, the\' lie in the 
plane of metamorphic foliation and plunge steeplv. 



Thickness determinations are only approximate since 
the strata have been thinned plasticall\', thickened by 
minor folds, faulted b\ numerous indeterminate Ccno- 
zoic normal faults, and obscured by extensive forestT^ 



120* 



, Lake Almanor 



Area of block diagram 
7 Taylorsville Area 



Permian? 8 Mesozoic 
Wedge 



Pyroclastic Sequence 
Shoo Fly Formation 




20 MILES 



Figure 1. Index map showing the relations of the Taylorsville area 
to the regional geology. Taylorsville (T), Quincy (Q), Wodes Lake (W), 
Sierra Butles (S), Downieville (D), North Fork American River where 
it crosses the top of the Shoo Fly Formation (N), Colfox (C), and 
Placerville (P) are represented on the map by letters. 



[173] 



174 



Gf.ol(x;y of Nortiiirn California 



Bull. 190 




Photo 1. View southeast acros! 
plate of the Toylorsville thrust, 
and Sierra Buttes Formations. Mt. 
lain by Shoo Fly of the upper plate. 



Indian Valley. Mt. Hough, right skyline, shows exposures of Peole and Arlington Formations of the lower 
rizzly Peak, left center skyline ridge, shows outcrops of upper plate Shoo Fly (Toylorsville Member), Grizzly, 
jra, left, exposes Jurassic rocks of the lower plate. Indian Valley is a complex graben. Camera site is under- 



At the present state of understanding of the evolu- 
tion of the Sierra Nevada, it appears that the Taylors- 
ville area lies athwart the Ncvadan structural axis. 
Farther south in the central Sierra Nevada, this axis 
is the locus of the batholithic complex. In the north, 
the axis is that of a major overturned syncline in which 
the entire know n stratigraphic section is involved. The 
Silurian, Mississippian, Permian, Triassic, and Jurassic 
and possibly the Devonian systems are represented. 
That the axis of batholithic activity coincides with a 
major syncline has been shown by Rinehart and others 
(1959, p. 941), and they have added the Ordovician 
and Pcnns>lvanian to the list of systems represented. 
All the pre-Nevadan stratified rocks of the Sierra Ne- 
vada may be interpreted as defining a faulted s_\n- 
clinorium (Bateman and others, 1963, p. D-6), for 
which the Nevadan sxnclinc is the axis. That the 



syncline was continuous involves interpolation of 17.^ 
miles, but the large outcrop breadth of 20 to ."JO miles 
combined with the continuity of the west limb in the 
interval of interpolation permit little room for alter- 
natives. A synclinal axis inferred by Taliaferro (1942, 
p. 99-100) in .\Iesozoic rocks west of Lake Tahoe 
de.scribes an intermediate point. 

This Nevadan s\ncline within the Taylorsville area 
is overturned to the northeast, and the overturned 
southwest limb has been thrust northeastward along 
the Taylorsville thrust onto the synclinal axis (see 
fig. 2). The upper plate can be traced onl\- 5-10 miles 
south of the 40th parallel before it is obliterated by 
granite or covered by Tertiar\' volcanic rocks. To the 
east, the moderately dipping normal limb contains only 
Mesozoic rocks as granite occupies the position where 
one would expect to find the Paleozoic section. To the 



1966 



McMath; Taylorsvillf. Area. Northern Sierra Nevada 



175 




Figure 2. Generalized btocic diagram of the Toylorsville area. 
Teeth denoting the upper plate of the Toylorsville thrust hove been 
employed even where the thrust has been offset by younger faults. 
The Kettle Formation, which mokes up much of the east limb of the 
Nevadon syncline, is designated by two approximately equivalent 
composite strotigraphic units: (1) Lilac through Moonshine Formations, 
and (2) unnomed dacite tuff-breccia through Cooks Canyon Formotion. 
Mt. Jura is indicated by a hochured circle in the half fenster de- 
scribed by the Toylorsville thrust, 

west, the Paleozoic of the overturned limb was faulted 
relatively upward along a steep strike fault, so that it 
is not now possible to trace the upper plate westward 
to its root zone. To the north, both limbs and the 
upper plate of the thrust are concealed by the Tertiary 
lavas of the Modoc Plateau. 

MAIN STRATIGRAPHIC SEQUENCES 

Three and probabl\' four demonstrable stratigraphic 
sequences make up the west limb of the Nevadan 
syncline (see fig. 3). "Sequence" is used in the re- 
stricted sense of a stratigraphic unit bounded above 
and below by major unconformities as proposed by 
Sloss and others (1949, p. 110) and as applied in the 
Cordilleran geosyncline by Silberling and Roberts 
(1962). Application of the "sequence" concept in the 
Taylorsville area has the further advantage that the 
unconformity-bounded units are lithogenetically dis- 
tinct from those above and below and also show a 
high degree of internal lithologic uniformity. 



vrn» n«TE 



Smirlnitr Forntlon •od 
Na»i«Tliui LlHitont 

UNCONFORUITY 



'V'*!"'— 



toedhut triinttoiit 



Ntli Feiut Ion 



?7^ 



Tiyler Forntlon 



■ iltilir Forut Ion 
UNCONFORUITY 



tiloo Fly Fofut lo 



17rt 



ModitKd from Turnir (IS97) 
Oo«n(tvllli OuodrongK 



G|-0L(K;V ok NoRTHlRN Cm. NORMA 

Thit Paptr 
Plott Upp«r Plott 

SWEARINGER 
HOSSELKUS 



Bull. 190 



Modidad Irom Dilllr (1906) 



SWF.ARINOER 



HOSSELKUS 



QUARTZ 
PORPHYRY 



Cortoniftroul \ CALAVERAS 



MILTON 
(in port) 





Carboftiftrou 



MONTGOMERY 

GRIZZLY 

METARHYOLITE 
■ Sitrro Butltl 



Figure 3. Pre-Jurassic correlation diagram for the Toylorsville area. Diller's column (on right) is modified In that his easti 
Meto-Andesite is inserted between his Peole and Reeve as demanded by his map relations, and his Robinson and Reeve Forma 
as Permian as emended by Thompson ond others (1946). Turner considered his augite porphyrite and quartz porphyry to be 
but they are shown as Permian as emended by Wheeler (1939). 



Prt-SilunOH 

rn belt of Taylor 
ions are indicated 
Juratrias in age. 



The lowest sequence consists of only two named 
formations, the Shoo Fly an(d the Taylorsville, which 
as mappecd by Diller hroadl\- represent respectivel)' 
lower and upper plate equivalents. Neither the lower 
limits nor the stratigraphic makeup of either unit is 
well known except in local areas. Because the Shoo 
Fly constitutes a large part of the outcrop belts for- 
merly referred collectively to the Calaveras Group 
(Clark and others, 1962, p. B-17), has a much greater 
extent along strike (100 miles or more), and shows 
promise of a more undisturbed and complete section 
(possibly 40,000 or 50,000 feet), the name Shoo Fly 
is provisionally extended to include the upper plate 
equivalents. Slate or phyllite, chert, and sandstone, the 
dominant components, contrast markedly with the 
unconformahl\- overlying pyroclastic sequence. Silu- 
rian fossils are present near the top. 

The second sequence, here termed the pyroclastic 
sequence, is found in both the lower and upper plates. 
It comprises eight formations consisting dominanth- 
(95-98 percent) of coarse water-laid, presumably 
marine, pyroclastic debris. It is nearly 25,000 feet 
thick and rests with angular unconformity on the 
Shoo Fly Formation. Two fossil localities, one near 
the middle and the other near the top, provide ages 
of Mississippian and Permian respectively. 

Informal reference to the pyroclastic sequence of 
Plumas County may prove useful; formal designation 
as the Plumas sequence would be desirable were it 
not for the possibility that a significant but undetected 
unconformity may intervene between dated Missis- 



sippian and Permian horizons. This sequence provides 
the ke\' to both the structure and the stratigraphy; 
hence, it has been the most thoroughh' studied and 
w ill be the principal subject of this paper. 

The third sequence, found only in the upper plate, 
contains strata of Triassic age only, hence may ade- 
quately be referred to as the Triassic sequence. It 
consists of two fossiliferous shelf-type formations, the 
Hosselkus Limestone and the Swearinger Formation. 
The Hosselkus rests with angular unconfonnity on 
the p\roclastic sequence. The Triassic sequence is 
rclativel)' thin, having a preserved thickness of only 
1,100 feet. However, its upper boundary is the trace 
of the Taylorsville thrust and it is locally cut out by 
a granitic pluton, hence it may well have been 
thicker. That the sequence probably is separated from 
the overh'ing sequence of Jurassic rocks by an un- 
conformity is inferred from relationships demon- 
strated farther south in the Sierra Nevada, where Clark 
and others (1962, p. B-19) have shown that the Lower 
Jurassic apparently oversteps about 400 feet of Upper 
Triassic(?) limestone within 1 mile. 

The fourth and youngest sequence consists only of 
Jurassic strata, hence again is adequateh' referred to 
as the Jurassic sequence. It is about 1 5,000 feet thick 
on the east limb and probabh- a little thinner on the 
\\'cst limb of the Nevadan syncline, and is known only 
in the lower plate. The widely known sections on 
Mount Jura have been referred to informall\- as the 
Mount Jura sequence for many \cars, but formal 
designation is considered neither nccessar\- nor de- 
sirable at this time. 



1966 



McMath: Taylorsville Area, Northern Sierra Nevada 



177 



The Jurassic sequence is dominated by volcanogenic 
roclcs, although epiclastic or reworked volcanic rubble 
and possibly nonvolcanic epiclastic material is inter- 
clalated here and there in the section. Indeed, orogcnic 
(polymictic) conglomerate is prominent in the upper 
part of the section, which may well be equivalent to 
the .Mariposa Formation of the foothill belt. Though 
the thickness of volcanic material suggests a deep 
trough, the general aspect is one of shoaling compared 
to that of the pyroclastic sequence. Perhaps this ex- 
plains why the Mount Jura sequence is unusualh' fos- 
siliferous for a eugeosynclinal sequence. 

Study of this sequence is incomplete; hence this 
treatment is little more than that of cataloging some 
of the more significant conclusions. 

REVISION OF PALEOZOIC STRATIGRAPHY 

The first geologic column of the area was provi- 
sionally set up by J. S. Diller (1892, p. .^72) in a pre- 
liminary account of the earliest s\'stematic study of 
the Taylorsville area. At the conclusion of intermit- 
tent field work, a modified and e.xpanded column was 
presented in a more complete paper (Diller, 1908, pi. 
4) and this is reproduced here as a part of figure 2. 

Major discrepancies between Diller's sequence and 
that of Turner (1897) in the adjacent Downieville 
.^0-niinute quadrangle are readiK' apparent despite the 
fact that Diller and Turner worked contemporane- 
ously on a project that involved both areas. For ex- 
ample. Turner's east-facing Juratrias sequence of 
quartz porphyry and augite porphyrite was described 
by Diller as west- facing Silurian (or pre-Silurian — 
text and plates are contradictory) metarhyolite and 
Carboniferous Taylor Meta-andesite, respectivelv. 

It is apparent that a major difficulty facing the early 
geologists was the lack of paleontologic dating. Only 
in light of later advances made in stratigraphy could 
the geology be confidently pieced together without 
the aid of fossils. These advances consist of the recog- 
nition of facies change and of the significance with 
respect to "top and bottom" of many small-scale 
(geopetal) structures, of which graded bedding is the 
most widespread and useful in this area. Drag folds 
and the angular relationship of cleavage to bedding 
have been of only secondary usefulness but in some 
places are misleading. 

The discrepancies between the Downieville quad- 
rangle and the Taylorsville area have now been largely 
reconciled as one result of drastic revision of Diller's 
structural and stratigraphic interpretation (fig. 2). 
Turner's east-dipping Juratrias volcanics have proved 
to be components of the late Paleozoic pyroclastic 
sequence and are overturned in the north part of the 
Downieville quadrangle. They continue northward 
into the Ta\'lorsville area retaining their overturned 
position and are there repeated by a major low-angle 
fault, the Taylorsville thrust. The repeated section is 
now also recognized in the northernmost part of the 
Downieville quadrangle. 



The lower part of Diller's Paleozoic sequence is 
based on apparent superposition above and below a 
single dated (fossiliferous) horizon, his Silurian Mont- 
gomery Limestone. His four older formations are now 
recognized to lie in the upper plate, and his three 
N'ounger formations constitute the lower plate. The 
uppermost formation of this sequence of seven as es- 
tablished b\' Diller was the Shoo Fly Formation. Be- 
tween the Shoo Fly and the upper part of his Paleozoic 
sequence, Diller indicates a break. Above this break, 
he placed the three fossiliferous (late Paleozoic and 
Triassic) formations of the upper plate in their cot^ 
rect relative order. Owing to paleontological control, 
he correctly recognized that these three fomiations 
were overturned, but he could not recognize that the 
seven below the break were also overturned. 

Durrell (/;/ Durrell and Proctor 1948, p. 171) de- 
scribed the first irrefutable contact relationship be- 
tween two of the formations of Diller's Paleozoic 
succession. Near Wades Lake in the center of the 
Downieville 30-niinute quadrangle, Diller's Shoo Fly 
Formation (equivalent to and having priority over 
Turner's Calaveras Formation) is clearly overlain with 
angular unconformity by the Sierra Buttes Formation 
(new name for the metarhyolite series of Durrell, 
quartz porph\ry of Turner, and metarhyolite of 
Diller). Detritus from the Shoo Fl\- is included in the 
basal conglomerate of the Sierra Buttes Formation and 
varies from place to place according to the underlying 
Shoo Fly rock type. Well exposed in the same area 
is a gradational contact between the Sierra Buttes and 
the overlying Taylor Formation, w hich Turner ( 1897) 
called augite porph\'rite. Graded bedding in both the 
Sierra Buttes and the Taylor confirm the succession. 

Reconnaissance by Cordell Durrell into the Taylors- 
ville area showed the same succession, but overturned: 
Shoo Fly, Sierra Buttes, and Taylor. The Sierra Buttes 
there is thin and was apparently overlooked by Diller. 
The Arlington Formation of Diller is adjacent to the 
Taylor and seemed to constitute a fourth and even 
younger fomiation of this sequence, for graded bed- 
ding indicated that it too is overturned. 

Subsequent field studies b\' the writer showed that 
Diller also failed to identif\- his Peak Formation be- 
tween the Arlington and Taylor. The contact between 
the Sierra Buttes and the Shoo Fly is clearly an angular 
unconformity in \\'hich a section of the Shoo Fly sev- 
eral thousand feet thick is truncated. No fossils that 
would permit an age assignment have yet been found. 
This is the lower plate succession and is tabulated in 
figure 2 for comparison with Diller's succession. 

Another Paleozoic succession, which differs from 
the lower plate succession owing to facies change, was 
faulted to the northeast along the Taylorsville thrust. 
Here again, graded bedding indicates that the succes- 
sion is generally overturned and that it faces to the 
northeast as does the lower plate succession. 

In the upper plate, the Taylorsville Formation of 
Diller occupies a stratigraphic position analogous to 



178 



CiKOUXiY OK NoRTllKKN CaI.IIORMA 



Bull. 190 



that held in the lower plate !)>• the Shoo Fl\' Forma- 
tion. The type Taxlorsville is here provisionally low- 
ered to member status within the Shoo Fl\-, and the 
name "Shoo Fl\" applied to all upper plate rocks 
lying unconformably below the pyroclastic sequence. 
The fossilifcrous Silurian Montgomery limestone beds 
are intercalated near the top of the Ta\lorsville Mem- 
ber. Diller (1908, p. 18-19) inferred an unconformity 
between the Montgomery and Taxlorsville on rather 
insecure evidence, and not knowing that the section 
is overturned, he a.ssigned a probably Devonian age 
to the Ta>lorsville. 

The ne.xt overlying formation in the upper plate is 
the Grizzl)-. .^n angular unconformity, the same as 
that between the Shoo Fl\- and Sierra Buttes Forma- 
tions, separates it from the underlying Ta\lorsvillc. 
The epiclastic Grizzly is interpreted as a basal unit 
deposited locall\- on an irregular erosion surface before 
the beginning of pyroclastic volcanism. It is overlain 
in turn by the pyroclastic Sierra Buttes Formation 
(Diller's metarhyolite). 

Xe.xt in succession, as in the lower plate, are the 
Taylor and Peale Formations. Diller called the Taylor 
of this block the Hull Meta-andesite and believed it 
to consist of Late Jurassic intrusive and volcanic rocks. 
It is. however, clearly pyroclastic and very much like 
the type Taylor except that it contains a wider variety 
of sills and dikes and additional varieties of meta-ande- 
site breccia. 

Conformably above the Peale lies the Goodhue 
Greenstone (new name) which Diller erroneoush- 
mapped as Taylor. The t\pe Taylor lies belo'v: the 
Peale. Aloreover, the rock of the Goodhue is readily 
distinguished from that of the type Taylor. Although 
the Goodhue ma\' be s\nchronous with the lower 
beds of the lower plate Arlington Formation, the rocks 
are lithologicall\- dissimilar. 

The next two formations are in the same order that 
Diller placed them: the Reeve Formation, then the 
Robinson Formation, both of which, however, are 
herein redefined. Some Reeve rock types are very 
distinctive, and their presence among the southeastern 
outcrops of the .Arlington Formation strengthens cor- 
relation of the upper and lower plates. The Robinson 
rock type is broadl\- comparable with that of the bulk 
of the .Arlington Formation of the lower plate. 

Diller (1908) included the Peale, Shoo Fly, Taylor, 
and .Arlington Formations in the Calaveras Group of 
supposed Carboniferous age. Turner (1897) included 
the direct extension of Diller's Reeve and Robinson 
in the Calaveras whereas Diller excluded them. Turner 
excluded the Ta\lor, and mapped much of the .Arling- 
ton or .Arlington equivalents in his jMilton Formation. 
The Shoo Fly together with its synonym, the Blue 
Can\'on Formation of the Calaveras Group (Lindgren, 
1900), have recently been excluded (Clark and others, 
1962, p. B-17), in part because rocks of Silurian age 
were specifically excluded from the Calaveras by 
Turner (1894, p. 446). Much of the type Calaveras is 



now known to be Mesozoic in age, and rocks that 
might be candidates for designation as t\pe Calaveras 
arc structurally very complex (Clark, 1964, p. 8, 12). 
.As at least a temporar\- expedient, the term "Cala- 
veras" will not be applied to an\- of the Taslorsville 
rocks. 

DESCRIPTION OF THE SEQUENCES 
Shoo Fly Formation 

The Shoo F"l\' Formation underlies ncarl\' the entire 
area of the largest and most continuous fault-bounded 
Paleozoic belt on the geologic map of California (in 
pocket), at least as far south as Placerville (see fig. I). 
.At the present stage of investigation, the Shoo Fly is 
formally a formation, but it certainK will eventuall)- 
be given formal sequence or at least group status. 
Three lithic units have already been discerned in the 
upper 10,000 feet of the lower plate. 

The uppermost of the three is greenstone, w hich is 
.^,000 feet thick and localh' truncated by the overlying 
p\ roclastic sequence. Clasts of the greenstone are in- 
corporated in the basal few feet of the p\roclastic 
sequence. 

The middle unit, about 2,000 feet thick, is almost 
certainly the lithic equivalent of the Taylorsville Mem- 
ber, which is in the upper plate and also about 2,000 
feet thick, although its base is faulted out (fig. 2). 
This unit in both plates underlies the pyroclastic se- 
quence with angular discordance, and it consists prin- 
cipall\- of laminated slate and ph\llite, thin beds of 
fcldspathic, p()ssibl\- tutTaceous graywacke, and minor 
intraformational breccia, chert, and limestone. 

The lower of the three units is similar to the middle 
hut also contains significant interbeddcd sandstone, 
which ranges from feldspathic gra\wacke to essen- 
tiall>- orthoquartzite, and some felsitic tuff or chert. 
It is .\000 feet thick. 

Below these three units, very thick undifferentiated 
slate and phyllite, chert, felsitic tuff, gra\wacke, and 
greenstone in variable but decreasing proportions in 
about the order listed comprise the bulk of the Shoo 
Fly of the lower plate. .A few spot observations sug- 
gest top is to the northeast for the entire lower plate 
.sequence. If the sequence is homoclinal and unfaulted, 
it is 40,000 to .>0,000 feet thick. 

The Shoo Fly of the upper plate includes, in addi- 
tion to the Ta\lorsville Member and most of the lithic 
t\pes found in the lower plate, a wide arra\- of dikes, 
sills, and small plutons that have hindered further 
stratigraphic subdivision. 

To the southw est, the Shoo Fly is generally bounded 
by a major serpentine-belt fault (Clark, 1960). How- 
ever, at the northwest end of the belt, just south of 
Lake Almanor, a thick east-facing Mesozoic and Per- 
mian(r ) wedge-shaped unit lies between the sepentine- 
belt fault and the Shoo Fly, and it must be separated 
from the Shoo Fl\- b\' another fault, probabl\- a thrust 
(see fig. 1). A fusulinid locality reported by Diller 
(1908, p. 23) to lie at the west margin of the Shoo 



1966 



McMath: Tayi.orsvii.i.i Aria, Northkrn Surra Niaada 



179 



Fly is probably at the base of the Permian(?) and 
Mesozoic wedge. 

No fossils unequivocally collected from the Shoo 
Fl>- of the lower plate are diagnostic of its age (see 
Clark and others, 1962, p. B-17). However, the Mid- 
dle(?) Silurian Montgomery Limestone of Diller is 
intercalated in the Taylorsville Member of the upper 
plate and this in turn is almost certainly equivalent to 
a unit in the upper part of the Shoo Fly of the lower 
plate. Tlius the Shoo Fly is at least in part Silurian. 
Owing to its very great apparent thickness, it probably 
includes rocks as old as Ordovician. 

Pyroclostic Sequence 

The p\rocIastic sequence includes in the lo\\er plate 
the Sierra Buttes, Taylor, Peale, and Arlington Forma- 
tions, and in the upper plate the Grizzly, Sierra Buttes, 
Ta_\'lor, Peale, Goodhue, Reeve, and Robinson Forma- 
tions. 

The p\'roclastic nature imparts a lithogenetic unity 
to the sequence and presents a strong contrast with 
the sequences above and belo\\-. A marked and signif- 
icant feature of the pyroclastic sequence is the relative 
sharpness and contrast owing to the change of chem- 
ical composition from one formation to the next. The 
gross succession of approximate rock types is dacite, 
andesite, latite, basalt or andesite, and dacite or silicic 
andesite. There is remarkably little intergradation be- 
tween these types. 

Contacts between formations of the sequence, how- 
ever, are generally gradational to some degree. Those 
that have not been demonstrated to be gradational, 
hence are conceivably unconformable, are the Taylor- 
Peale, Peale-Arlington, and Reeve-Robinson. Localh- 
there are breccias at the Goodhue-Reeve contact that 
are intermediate in chemical composition between the 
t\'pical Goodhue and Reeve breccias, suggesting a 
transition from one to the other; however, this is con- 
sidered only weak evidence for a gradational contact. 
Clearl\-, there is a possibility that an unconformit\' 
lies undiscovered above the Peale of the lower plate, 
and above the Goodhue of the upper plate, so that 
there may be only partial equivalence of the Arlington 
with the Goodhue, Reeve and Robinson. 

Grizzly Fonnation. Found only on the upper 
plate, the Grizzly Formation is a thin epiclastic unit 
probably filling low places on the erosion surface on 
which it was deposited. It consists principally of black 
laminated slaty shale and blocky siltstone, and quartz- 
rich graywacke. It is generally abundantly interlaced 
with sills so that a true sedimentary thickness is dif- 
ficult to measure, but the maximum is probably close 
to 200 or 300 feet. Arkose occurring 20 miles south, 
where Durrell (Durrell and Proctor, 1948, p. 171) 
first demonstrated the unconformity, may be nearl>- 
correlative. 

Sierra Buttes Formation. The name Sierra Buttes 
Formation is here proposed for Turner's quartz por- 
phyry of the Sierra Buttes (1894, p. 483; 1896, p. 646; 



1897, p. 2), Diller's metarhyolite (1908, p. 81) and 
quartz porphyry (1895), and the metarhyolite series 
of Durrell and' Proctor (1948, p. 171). The Sierra 
Buttes (fig. 1), the highest and most distinctive peaks 
composed of the rocks of this formation, are in the 
south part of the Downieville 30-minute quadrangle. 
.■\ t\pe section was not designated, but a representa- 
tive section can be seen in the vicinity of Long Lake 
and Wades Lakes seven miles northwest of the Sierra 
Buttes. The thickness of the formation is 4,000 to 
5,000 feet but decreases to less than 1,000 feet in the 
northwest part of the lower plate. Excluding dikes 
and sills, the formation consists principally of bedded 
quartz keratoph\re breccia, tuff, and perhaps some 
flows, whose gross chemical composition is probably 
closer to dacite than to rhyolite. .Minor chert, slate, 
and rare limestone with fragments of marine fossils 
also are present. 

Taylor Forviatioii. The Ta\lor Meta-andesite of 
Diller (1908, p. 83), or the augite porphyrite of 
Turner (1897), is characterized by augite andesite 
breccia, tuff-breccia, tuff, subordinate flows, minor 
black tuffaceous slate, and crinoidal limestone. Its 
thickness is about 8,000 feet. The size of the blocks in 
the breccia increases to 6 to 8 feet in the Downieville 
30-minute quadrangle, hence the source probably lay 
in that vicinity. 

Peale Formation. Dark quartz keratoph>rc flows 
and co-magmatic tuff-breccia and tuff, probably ma- 
rine, characterized by pink alkali feldspar phenocrysts, 
dominate the lower half of the Peale Formation. The 
upper half consists principally of varicolored "ribbon" 
chert, slate, tuffaceous sandstone, and intraformational 
slump breccia. Maximum thickness approaches 2,500 
feet. All known manganese deposits in the northeast- 
ern Sierra Nevada are in the middle of the Peale For- 
mation. 

Arlington Formation. Countless varieties of ande- 
sitic and dacitic tuff and tuff-breccia, water-laid and 
well graded, and interbedded slate and minor volcanic 
conglomerate-breccia comprise the Arlington Forma- 
tion, w hich is recognized onl_\' in the lower plate. In- 
tercalated breccia typical of the Reeve Formation in- 
dicates at least broad equivalence of the Arlington 
with the Goodhue, Reeve, and Robinson succession. 
The apparent thickness is 8,000 feet. 

Goodhue Greenstone. The name Goodhue Green- 
stone is here applied to a distinctive pyroclastic brec- 
cia which Diller (1908, p. 84 and p. 3) called Taylor 
and referred to as lavas. The Goodhue, restricted to 
the upper plate, overlies the Peale Formation, whereas 
the Taylor underlies the Peale. Andesite of the Taylor 
is characterized by augite phenocrysts, whereas ande- 
site or basalt of the Goodhue contains augite plus 
a relict second ferromagnesian phenocryst now rep- 
resented by magnesian chlorite or a serpentine mineral. 

Derivation of the name is from the Goodhue home- 
stead on Ward Creek, in the NE '/^ SW 'X SW 'X sec. 



ISO 



GfOUKiY OK NoRIHIRN CaIIKORMA 



Bill 



190 



14, T. 25 N., R. 11 F. The building is shown on 
earlier topogrnphic maps, though not on the latest 
(Kettle Rock, 1950). The type locality includes the 
east slope of Pcaie Ridge immediately west of Ward 
Creek, and the type section is in the NE% sec. 22, T. 
25 N., R. 11 E. The thickness of the Goodhue Green- 
stone is 1,500 feet. 

Reeve Fonnation. Keratoph\re breccia and tuff, 
here and there fossiliferous, and minor fusulinid lime- 
stone and chert pebble conglomerate comprise the 
Reeve Formation as redefined here. Diller apparently 
attempted to map the "sedimentary" tufif and lime- 
stone units in his Robinson Formation and the "igne- 
ous" breccia in his Reeve. More logical units are ob- 
tained b\' including ail rock t\pes intercalated in the 
breccia as a part of the Reeve, and restricting the 
Robinson to a distinctl\- different succession of vol- 
canogenic rocks which Diller also included in his 
Robinson Formation. The Reeve is characterized b\' 
plagioclase phenocr\sts having major diameters of 10 
to 20 millimeters, whereas those of the Robinson do 
not exceed 2 millimeters. The maximum apparent 
thickness is about 2,000 feet. 

Rob'uisoii Fonnatioii. As redefined above, the Rob- 
inson consists of andcsitic conglomerate-breccia, vol- 
caniclastic calcareous sandstone, slate, and minor lime- 
stone. The maximum thickness is 700 feet. Fossils, 
obtained from conglomeratic beds, are Paleozoic and 
suggestive of a Permian age. 

Age of the Pyroclastic Sequence 

Only two horizons are dated b\' diagnostic faunas. 
The lower is at about the middle of the Peale Forma- 
tion, and is at a localit\- reported b\' Diller (1908, p. 
24). G. A. Cooper kindl\' studied the brachiopods 
from a new collection and determined them to be 
Early Mississippian in age (written communication, 
1965). 

The upper fossiliferous horizon is broadly in the 
middle of the Reeve Formation, which as re-defined 
includes most of the localities Diller (1908, p. 27-28) 
included in his Robinson Formation. The most diag- 
nostic fossils are large fusulinids, which, however, are 
too recry.stallized to identify specifically. Because of 
their large size, they are certainl\' Permian. Thompson 
and others (1946, p. II) state that Fusiiliiia eloiii^ata 
Shumard listed from the "Robinson locality" by Diller 
is probabl\- I'ara^usiiliiia. 

A Permian age was formerly conceded for the 
Taylor (specifically for the augite porphyrite of Tur- 
ner) because a mold of Hclicoprioii sicrreiisis discov- 
ered in Pleistocene till was supposedly derived from 
Turner's augite pf)rphyrire (VVheeler, 1939, p. 107). 
However, in the glacial basin from which the till must 
have been derived. Turner included Peale and prob- 
ably Arlington rock t\pcs in his augite porphyrite. 
Moreover, a pctrographic description of the matrix 
made for Wheeler compares neither with the Taylor 



near Peale, but with the .Arlington. Thus a Permian 
age for part of the Arlington is stronglx' suggested. 

0\\ ing to the discovery of probable Devonian fos- 
sils in limestone associated with volcanics in the foot- 
hill belt (I,. D. Clerk, written communication, 1959), 
a Devonian age for the Sierra Buttes and Ta\'lor is 
possible. 

Regional Relations of the Pyroclastic Sequence 

Most units of the pyroclastic sequence continue at 
least 40 miles southeast along the west limb of the 
Ncvadan syncline to the North Yuba River and Mil- 
ton Reservoir. In some places all the .Milton Formation 
of Turner (1897) consists of rock types characteristic 
of the Peale, perhaps the Goodhue, and certainly of 
the Reeve. Farther south the p\roclastic sequence 
must be truncated by its bounding unconformity be- 
cau.se at North Fork American River, about 50 miles 
south of the Taylorsville area, Triassic(?) rests di- 
rectly on the Shoo Fly Formation (Clark and others, 
1962, p. B-18). Possibly correlative Pennsylvanian and 
Pcrmian(r) strata in roof pendants 175 miles south are 
nonvolcanic (Rinehart and others, 1959); these pen- 
dants define the east limb of the Nevadan syncline. 

Correlation onl\- on the grounds of lithlogic simi- 
larity of the component formations of the pyroclastic 
sequence with specific formations outside the immedi- 
ate outcrop belt ma\- well pro\e impossible, .•\lthough 
the characteristic rock t\pes of the sequence are 
rcadil\- identified for 65 miles along strike, at the 
northern end of the belt constituent fragments become 
so fine grained that identification becomes partl\- sub- 
jecti\e. If there has been appreciable telescoping along 
thrust faults farther west, individual lithic types prob- 
abl\' do not persist across faults. However, it may 
prove feasible to find equivalents of the pyroclastic 
sequence in a gross manner, assuming that the vol- 
canic episode responsible for the sequence was areall>' 
widespread. Perhaps the unfossiliferous Kanaka and 
Tightner Formations of Ferguson and Gannet (1932) 
and the Tightner of Chandra (1961, p. 12), which 
contain abundant volanic material, are broadly equiva- 
lents. However, these formations are separated from 
the outcrop belt of the pyroclastic sequence b\- a ma- 
jor scrpcntine-bclt fault zone and are 60 miles south 
of the Ta\lorsville area. Still farther south, in the 
Foothill belt, Permian limestones included in the Cala- 
\eras Formation are associated with \()lcanic rocks 
(Clark, 1964). 

Correlation with late Paleozoic rocks outside the 
Sierra Nevada cannot be attempted even on a gross 
lithologic basis because of facies changes, and is there- 
fore dependent on paleontologic dating. The nearest 
correlatives in all directions except to the southeast 
contain appreciable volcanic constituents and gener- 
ally are as sparsely fossiliferous as the late Paleozoic 
of the Taylorsville area. For the interested reader, the 
more recent pertinent papers are by Coogan (1960), 



1966 



McMath: Tayi.orsvii.ik Arka, Northern Sikrra Nkvada 



181 



Albers and Robertson (1961), and Silberling and 
Roberts (1962). 

Triassic Sequence 

Rocks of the Triassic System, consisting of the t\pe 
Hosselivus Limestone and the Swearinger Formation, 
are exposed in the Tayiorsvilie area only on the frontal 
margin of the upper plate of the Tayiorsvilie thrust. 
The\' are relatively thin, rather abundantly fossilif- 
erous compared to subjacent strata, and in contrast 
to all other systems in the area, quite free of identified 
volcanic debris. Their setting was more that of the 
quiescent shelf than of the mobile eugeosyncline that 
both preceded and followed their deposition. The\- 
rest with angular unconformity on both known and 
questionable Permian strata, and their upper boundary 
is the trace of the Tayiorsvilie thrust. Together with 
the Tayiorsvilie thrust, they are complexly folded, lo- 
cally involuted, and are thoroughl>- hornfelsed where 
an adjacent granitic pluton has intruded them. 

Diller (1892) and Hyatt (1892) named the two 
iithic units the Hosselkus Limestone and the Swear- 
inger Slate, and Hyatt dated them as Late Triassic. 
The Swearinger dips under the Hosselkus and was 
therefore presumed to be the older, but Diller (1908, 
p. 33) subsequently concluded that the Swearinger is 
the younger and that both are therefore overturned.' 

On the basis of sedimentary structures indicating 
the Swearinger is not overturned, and a faulted contact 
between the Triassic and Permian(?), McMath (//; 
Reeside and others, 1957, p. 1470) reversed the se- 
quence to agree with Diller's original interpretation. 
Subsequent field stud\' showed the sedimentary struc- 
tures to be contained in involuted beds of the Robin- 
son Formation faulted into juxtaposition with the 
Swearinger. The faulted contact between the Robinson 
and the Hosselkus must be an example of an uncon- 
formity "unglued" by local flexure folding — an incip- 
ient decollement — because a definitive outcrop later 
discovered outside the zone of intense folding showed 
a depositional contact. History has repeated itself: the 
sequence is once again reversed. May this Triassic 
section forever rest undisturbed upside down! 

The contact between the Hosselkus and Swearinger 
is gradational. Representative thicknesses are about 200 
feet for the Hosselkus and perhaps 900 feet for the 

^ Inversion of the apparent sequence was based on correlation with an 
Upper Triassic section, also described by Diller (1906), in Shasta 
County about 100 miles to the northwest. There, two shale forma- 
tions lithologically comparable to the Swearinger lie both above and 
below a limestone to which J. P. Smith (1894, p. 604-609) applied 
the name "Hosselkus." He correlated the limestone and the under- 
lying shale unit — the Pit Formation — with respectively the type 
Hosselkus and the type Swearinger. The apparent sequence of the 
two sections is the same. This correlation was discredited when 
Smith (1898. p. 778) subsequently correlated the shale above the 
"Hosselkus" — the Brock Shale — with the Swearinger. The faunal tie 
of the Swearinger witli the Brock proved to be closer than with the 
Pit Formation. But the name Hosselkus was retained for the lime- 
stone. And this was done despite the fact that the t\-pe Hosselkus 
was dated so inexactly that Diller subsequently felt free to shift it 
from above the Swearinger to below. Thus Diller inverted the 
apparent sequence of the type Hosselkus and Swearinger to make 
them agree with the supposedly equivalent Shasta County section. 
He did not question the initial correlation of the type Hosselkus 
with the Shasta County limestone. Correlation of these two lime- 
stones is not established even today according to N. J. Silberling 
(oral communication, 1965). Nonetheless, Diller was correct in 
reversing the sequence. 



Swearinger, but flowage during folding, incomplete 
resolution of structure, and other factors already cited 
preclude meaningful measurements. 

The Hosselkus consists largel\' of dark gray or black 
aphanitic limestone which weathers light gra\', and is 
thinly bedded to laminated where bedding is visible. 
Beds of calcarenite, commonly containing rounded 
quartz grains, crop out near both margins. Locally 
abundant white splotches generally represent sheared- 
out and recrystallized fossils. 

Black, calcareous, laminated hornfels having little 
relict fissility characterizes the Swearinger Formation. 
Thin black argillaceous limestone, quartzose sandstone 
beds, two of which are imperfectly graded and indi- 
cate top to the east, and a little conglomerate are also 
present. 

Age assignments for the two formations have not 
changed appreciably from those given b\' 'Hyatt 
(1892, p. 399): Late Triassic and specifically Xorian. 
.\ccording to G. E. G. Westermann ( 1962, p. 753), the 
age of the beds bearing Monotis siihcirciiUnh Gabb is 
probably late Norian. Westermann further postulates 
that Monotis lived in shallow water, perhaps attached 
to seaweeds. 

Correlation of at least the Movotis beds of the 
Swearinger with part of the Brock Shale of Shasta 
County seems well established (Smith, 1927). Other 
Late Triassic or supposcdl\- Late Triassic formations 
that may correlate with either or both the Hosselkus 
and Swearinger are the Pit Formation and "Hosselkus" 
Limestone of Shasta County (Diller, 1906; Smith, 
1927; Sanborn, 1960; Albers and Robertson, 1961), the 
Cedar Formation, which is a few miles west of the 
Tayiorsvilie area (Smith, 1894; Diller, 1895), limestone 
on the North Fork American River, 50 miles to the 
south (Clark and others, 1962), and possibly part of 
the Milton Formation 30 miles south in the Downie- 
ville quadrangle (Turner, 1897). 

It is conceivable that the boundary between the 
Triassic and Jurassic sequences is exposed but not yet 
recognized. The upper part of the Swearinger con- 
tains considerable hornfelsed feldspathic sandstone 
that could readih- mark the base of the Jurassic. Al- 
ternatively, if the uppermost part of the Triassic se- 
quence were volcanic, it is possible that a horizon in 
the oldest known Jurassic formation, the Lilac, marks 
the boundary. A third possibility, at least as likely as 
the first, is that the Triassic-Jurassic boundary may 
lie in dark hornfels, which underlies the more obvi- 
ously volcanic part of the Kettle Formation at its 
eastern border. 

Jurassic Sequence 

The marine Jurassic section exposed principally on 
.Mount Jura has long been an outstanding geologic at- 
traction of the Tayiorsvilie region. Like the late Paleo- 
zoic sequence, it is volcanogenic and it is structurally 
and stratigraphicall\' ncarl\- as complex, but on a 
smaller scale. "It is structurally so complex that a 
formation placed at its base b\- one of the t\\ o chief 



182 



Geology of Northkrn California 



Bull. 190 



authorities is placed by the other authority at its 
top" (Reed, 1943, p. 106). Owing to the relative abun- 
dance of fossils and of distinctive rock t\pes, the prin- 
cipal investigators, J. S. Diller (1892, 1908) aided by 
.\lpheus Hyatt (1892), and C. H. Crickmay (1933) 
were induced to erect 14 formations; two more arc 
recognized in the present study. One is an unnamed 
dacite tuff-breccia former!)- regarded as intrusive, and 
the other, the Kettle Formation (Kettle Meta-andesite 
of Diller), was regarded by Diller (1908, p. 84-85) as 
Carboniferous. 

Crickmay published only a tabular summary of his 
restudy of the Jurassic sections. In such a brief treat- 
ment of his results, he was not able to marshal the 
evidence for his changes, hence some of them were 
not readily accepted. Though the present study of the 
Jurassic is incomplete, and revision will not be docu- 
mented, an advance sumn>ar\' in support of Crickmav's 
stratigraphic succession seems warranted. 

The Kettle Formation and the overlying Trail For- 
mation of Diller (which is equivalent to Crickmay's 
Lucky S, Trail, and possibly Combe Formations) con- 
stitute the normall\' dipping east limb of the Nevadan 
syncline. Although the Kettle is cut out on the north- 
east by a granitic pluton, the total thickness of the two 
formations is more than 15,000 feet. The sections on 
Mount Jura are equivalent to the Kettle in whole or 
in part, are similarly overlain by Diller's Trail Forma- 
tion (but mapped by Diller in his Foreman Forma- 
tion), and constitute the western and overturned limb 
of the Nevadan s\ncline. Thc\' are repeated by a 
complicated fault system that appears to be essentialh 
a folded gravity-slide thrust. The upper plate of the 
Taylorsville thrust largely conceals the synclinal axis, 
and completely conceals the lower stratigraphic 
boundar\' of the Mount Jura sections. 

Crickmay (1933, p. 897) stated that his oldest Juras- 
sic formation, the Lilac, rests on Middle Triassic vol- 
canics. Because Upper Triassic rocks were presumably 
derived b\- thrusting from the same limb of the Neva- 
dan s\'ncline as the Mount Jura sections, it is sug- 
gested that the volcanics in question are even older 
Jurassic, and that Upper Triassic rocks underlie the 
volcanics but are concealed by the upper plate of the 
Taylorsville thrust. 

The Mount Jura sequence is outlined in the table 
below. Thicknesses are generally those listed by Crick- 
may. 

The Combe Formation of Crickmay has not yet 
been identified. Its age is controversial because Crick- 
may dated it as younger than the Nevadan orogeny. 

The Kettle Formation is equivalent to the Cooks 
Canyon and earlier formations, and includes the same 
gross lithic types. A dacite tuff-breccia in the middle 
of the formation is assumed to be the same as the 
unnamed dacite tuff-breccia of the Mount Jura sec- 
tion, and the block diagram has been constructed on 
this assumption. The total thickness of the Kettle is 



Jurassic stction on 






Mount Jura 






Trail Formation 


Polymictic conglomerate, volcaniclastic sand- 
stone, tuff, and mudatonc. 


4.000 


Lucky S Formation 


Black, plant-bearing sUte. fine quartz-rich gray- 

wacke. and pebble conglomerate. 
Andcsitic and dacitic tun-breccia and tuff, vol- 


1.500 


Cooks Canyon Forma- 


1.900 




canic conglomerate, volcaniclastic sandstone 
and mudstone. 




Foreman Formation — 


Dark-gray fossilifcrous shale, mudstone. and fine 
volcaniclastic sandstone. 


350 


North Ridge Formation 


Andesitic tuff-breccia and tuff. 


200 


Hinchman Formation.. 


Fossilifcrous conglomerate-breccia and volcani- 
clastic sandstone. Includes part of Bicknell 
Sandstone of Diller. 


160 


Hull Formation 


Andesite tuff-breccia and tuff. Includes part of 
Bicknell Sandstone of Diller. 


700 


Unnamed Dacite Tuff- 
breccia 
Moonshine Formation. 


Biotitc-hornblcndc dacite tuff-breccia and tuff. 


600 


Volcanic conglomerate, red shale, and tuff. Fos- 


300 




silifcrous. 




Mormon Formation... 


Volcanic conglomerate, fossilifcrous volcaniclas- 
tic sandstone, and black Pojidonia shale. 


950 


Thompson Formation.. 


Red fossilifcrous tuff, limestone, dacite breccia 
and lava, and volcanic conglomerate. 


400 


Fant Mcta-andcsitc — 


Augite andesite flows bearing large feldspar phe- 
nocrysts. and minor red tuff. 


800 


Harddrave Sandstone, 


Red volcaniclastic sandstone, highly fossiliferous. 


400 


Mlac Formation 


Dark-gray calcareous sandstone and mudatonc. 
dacite flo\v-brcccia{?) and tuff. Fossilifcrous. 


725 




Total 


13.000 



about 10,000 feet, and Callovian (Late Jurassic) am- 
monites occur about 2,000 feet below the top (Imlay, 
1961, p. D-9). It is conceivable that the Kettle extends 
down to the Triassic or even the Paleozoic. 

Confirmed or only mildly controversial ages for the 
Jurassic range from medial Early Jurassic (see Imlay, 
1952) for the Hardgrave Sandstone and Lilac Forma- 
tion to early Late Jurassic (Callovian) for the Fore- 
man Formation (Imlay, 1961, p. D-9). 

An interpretive note on the Jurassic conglomerates 
seems desirable. Several conglomerate beds in the more 
obviously volcanic section below the Lucky S Forma- 
tion show features that suggest they are not to be 
interpreted in terms of subaerial erosion as a result of 
diastrophic uplift. Such conglomerates are highly len- 
ticular, the rounded clasts are volcanic, and some in- 
clude angular, penecontemporaneously deformed intra- 
formational blocks as long as 12 feet. Slump structures 
are locally abundant in associated sandstone beds. 
These conglomerates are therefore interpreted as rep- 
resenting stream-mouth gravels that accumulated near 
the shores of volcanic islands, and from time to time 
slumped farther seaward. Conglomerate beds in the 
Trail Formation on the other hand are more continu- 
ous, associated with cross-bedded sandstone, and con- 
tain in addition to volcanic clasts, numerous types of 
sandstone, tuff, shale, and chert, all rounded. The Trail 
conglomerates are therefore orogenic in the usuall>' 
accepted sense. 

ACKNOWLEDGMENTS 

The author wishes to express deep appreciation for 
the generous financial aid extended by the Shell Com- 
panies Foundation Fellowship Committee, the Geo- 
logical Society of America (Grant No. 652-54-s56), 
the University of California at Los Angeles, the Uni- 
versity of Oregon, and the National Science Founda- 
tion. Among numerous individuals who gave gener- 



1966 



McMath: Tayi.orsvili.f, Area, Northern Sierra Nevada 



183 



ously of time and advice, Cordell Durrell and John C. 
Croweil deserve special mention. Part of the paper is 
condensed from a Ph.D. dissertation submitted to the 



Graduate Faculty of the University of California, Los 
Angeles. The Continental Oil Company provided gen- 
erous aid in the preparation of the manuscript. 



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northern Sierra Nevada, California: U.S. Geol. Survey Prof. Paper 

450-B, art. 6, p. B15-B19. 
Coogon, A. H., 1960, Stratigraphy and paleontology of the Permian 

Nosoni and Dekkos Formations (Bollibokka Group): California Univ. 

Pubs. Geol. Sci., v. 36, no. 5, p. 243-316. 
Coombs, D. S., 1960, Lawsonite metagraywackes in New Zealand: Am. 

Mineralogist, v. 45, nos. 3-4, p. 454-455. 
1961, Some recent work on the lower grades of metomorphism: 

Austrolion Jour. Sci. v. 24, no. 5, p. 203-215. 
Crickmay, C. H., 1933, Mount Jura investigation: Geol. Soc. America 

Bull., V. 44, no. 5, p. 895-926. 
Diller, J. S., 1892, Geology of the Toylorsville region of Califo 

Geol. Soc. America Bull., v. 3, p. 369-394. 
1895, Description of the Lassen Peak quad 

Geol. Survey Geol. Atlas, Folio 15. 
1906, Description of the Redding quadn 

Geol. Survey Geol. Atlas, Folio 138. 
1908, Geology of the Toylorsville 

Survey Bull. 353, 128 p. 

Durrell, Cordell, and Proctor, P. D., 1948 

Howley and Spencer Lakes, Sierra County, California 

Div. Mines Bull. 129, pt. L, p. 165-192. 
Ferguson, H. G., and GanneH, R. W., 1932, Gold quartz veins of the 

Alleghany district, California: U.S. Geol. Survey Prof. Paper 172 

139 p. 

Hyatt, Alpheus, 1892, Jura and Trias at Toylorsville, California: Geol 
Soc. America Bull, v. 3, p. 395-412. 



regi( 

angle, California: U.S. 

ngle, California: U.S. 

region, California: U.S. Geol. 

deposits near Lake 
California 



Imlay, R. W., 
America, ex 
p. 953-992. 



1952, Correlation of the Jurassic formations of North 
ilusive of Canada: Geol. Soc. America Bull., v. 63, no. 9, 



1961, Late Jurassic ammonites from the western Sierra Nevada, 

California: U.S. Geol. Survey Prof. Paper 374-D, p. D1-D30. 
Lindgren, Waldemor, 1900, Description of the Colfox quadrongle, 

California: U.S. Geol. Survey Geol. Atlas, Folio 66. 
Reed, R. D., 1943, California's record in the geologic history of the 

world: California Div. Mines Bull. 118, p. 99-118. 
Reeside, J. B., Jr., chm., and others, 1957, Correlation of the Triossic 

formations of North America exclusive of Canada, with a section on 

Correlation of continental Triossic sediments by vertebrate fossils, 

by E. H. Colbert and J. T, Gregory: Geol. Soc. America Bull., v. 68, 

p. 1451-1513. 
Rinehort, C. D., Ross, D. C, and Huber, N. K., 1959, Paleozoic and 

Mesozoic fossils in a thick stratigraphic section in the eastern Sierra 

Nevada, California: Geol. Soc. America Bull., v. 70, no. 7, p. 941-945. 
Sanborn, A. F., 1960, Geology and paleontology of the southwest 

quarter of the Big Bend quadrangle, Shasta County, California: 

California Div. Mines Spec. Rept. 63, 26 p. 
Silberling, N. J„ ond Roberts, R. J., 1962, Pre-Tertiary strotigraphy and 

structure of northwestern Nevodo: Geol. Soc. America Spec. Paper 

72, 58 p. 
Sloss, L. L., Krumbein, W. C, and Dapples, E. C, 1949, Integrated 

facies analysis, in Longwell, C. R., chm.. Sedimentary facies in 

geologic history: Geol. Soc. America Mem. 39, p. 91-124. 
Smith, J. P., 1894, The metamorphic series of Shasta County, California: 

Jour. Geology, v. 2, p. 588-612. 
1898, Geographic relations of the Trios of California: Jour. 

Geology, v. 6, p. 776-786. 
1927, Upper Triossic marine invertebrote faunas of North America: 

U.S. Geol. Survey Prof. Paper 141, 262 p. 
Taliaferro, N. L., 1942, Geologic history and correlation of the Jurassic 

of southwestern Oregon and California: Geol. Soc. America Bull., 

V. 53, no. 1, p. 71-112. 
Thompson, M. L., Wheeler, H. E., ond Hozzord, J. C, 1946, Permian 

fusulrnids of California: Geol. Soc. America Mem. 17, 77 p. 
Turner, H. W., 1894, Rocks of the Sierra Nevada: U.S. Geol. Survey 

Ann. Rept. 14, p. 435-495. 
1896, Further contributions to the geology of the Sierra Nevada: 

U.S. Geol. Survey Ann. Rept. 17, p. 521-762. 
1897, Description of the Downieville quadrangle California: U.S. 

Geol. Survey Geol. Atlas, Folio 37. 
Westermann, G. E. G., 1962, Succession and variation of Monofis and 

the associated fauna in the Norian Pine River Bridge section, British 

Columbia (Triossic, pelecypodo): Jour. Paleontology, v. 36, no. 4, 

p. 745-792. 
Wheeler, H. E., 1939, He/icoprion in the Anthrocolithic (late Paleozoic) 

of Nevada and California, and its strotigrophic significonce: Jour. 

Paleontology, v. 13, no. 1, p. 103-114. 



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Gkologv ok Northkrn Cai.iidrma 



Bull. 190 




TERTIARY AND QUATERNARY GEOLOGY 
OF THE NORTHERN SIERRA NEVADA 



cordell durrell 
California, Davis, California 



For purposes of this paper the southern limit of the 
northern Sierra Nevada is arbitrarily taken as the route 
of U.S. Highway 40, also known as Interstate 80, from 
Sacramento via Truckee, California, to Reno, Nevada. 
On the north the limit, equally arbitrary, is set as the 
line along which the pre-Tertiary metamorphic and 
plutonic "bedrock series" of the Sierra Nevada disap- 
pears beneath volcanic rocks of probable Pliocene age. 
This is roughly an arc extending from near Oroviile 
in the Sacramento Valley to Susanville (fig. 1). The 
western limit is, of course, the Sacramento V^alley. 
The eastern limit is the accepted geographic boundary 
which follows the Honey Lake fault scarp southeast- 
ward from Susanville to near \'erdi, Nevada, on High- 
way 40. 

Thus defined, the northeastern part includes a por- 
tion of the Basin and Range province. The Pacific 
drainage divide which follows the crest of the Sierra 
Nevada from its southern end northward along the 
west side of Lake Tahoe turns sharply east just a few 
miles north of Truckee on High\\'ay 40. It passes 
around the south and east sides of Sierra Valley and 
then follows the crest of the Honey Lake fault scarp 
to beyond Susanville (fig. 1). The crest of the nearly 
monolithic fault block which is the Sierra Nevada 
proper, continues northwestward from Truckee and 
passes west of Sierra Valley, Mohawk Valley, Spring 
Garden, American \^alle\', and continues in the direc- 
tion of iMount Lassen (fig. 1). 

The region bet\\'een the crest of the Sierra Nevada, 
as defined above, and the Pacific drainage divide in- 
cludes the valle\'s named above, other similar valleys 
all of which are basins whose origin is due to faulting, 
and the Grizzly and Diamond Mountains. This region 
has basin and range structure, but it is not within the 
Great Basin as it is drained to the Pacific Ocean by 
the headwaters of the Aliddle and North forks of the 
Feather River, both of which cross the Sierra Nevada. 

PREVIOUS WORK 

The early literature that relates to this area is sur- 
prisingly large, but is well summarized in t\vo papers 
by Henry Turner (1895, 1896). The first important 
maps are those of Turner and Lindgren of the Downie- 
ville, Bidwell Bar, Truckee, Colfa.x, and Sacramento 
quadrangles published as folios of the Geologic Atlas 
of the United States. The monograph on the Tertiary 



gravels (Lindgren, 1911) was the last general work to 
be published. Later work was more detailed and con- 
fined to small areas. Over most of the area the best 
information available is still that by Lindgren and 
Turner. Reconnaissance mapping by the California 
Division of Mines and Geology has filled in previously 
unstudied areas for the preparation of the new State 
geologic map sheets published at a scale of 1:250,000. 
The reader is referred to the Westwood and Chico 
sheets of this series for general coverage of the area 
under discussion. 

GEOLOGY 

Introduction 

The Tertiary and Quaternary rocks of the northern 
Sierra Nevada include marine and continental sedi- 
ments of volcanic and nonvolcanic origin, lava flows, 
and intrusions. Their ages range from middle Eocene 
to Recent. Marine sediments are confined to a few 
small areas at the western edge of the range. Conti- 
nental sediments within the range are fluviatile, lacus- 
trine, glacial, and volcanic. The volcanic sediments are 
volcanic fanglomerate, conglomerate, sandstone, and 
mudstone; tuff, tuff breccia, mudflow breccia, and 
ignimbrite. Lavas are olivine basalt and andesite, as are 
also plugs and dikes. Lava flows are far less abundant 
than clastic volcanic rocks so that stratigraphic prob- 
lems are as important as petrologic problems. 

STRATIGRAPHY 
Cretaceous 

Just north of the area under discussion and near the 
margin of the Sacramento \"alley are marine Upper 
Cretaceous sandstones, shales, and conglomerates. The 
tvpe section of the Chico formation on Chico Creek 
ranges in age from probable late Coniacian to middle 
Campanian (Popenoe, 1960). The section is 4,000 feet 
thick, dips gently westward, and rests on the "bedrock 
series" of the Sierra Nevada. Beds of Upper Cretaceous 
age also occur at Pentz in Butte County, and at Fol- 
som, just south of the limit of the area (fig. 1). This 
distribution suggests that the edge of Cretaceous beds 
beneath the Sacramento \'alle\' is not far from the 
edge of the mountain range. The Upper Cretaceous 
shoreline paralleled the trend of the range and was 
for a time at the present limit of outcrop, but there 
is no information as to how far east younger Creta- 
ceous beds may have lapped on to the "bedrock series." 



185: 



186 



Geology of Xorthfrn California 



Bull. 190 




Figure 1. Mop of the northern Sierro Nevada, showing geogrophic feoturej, distribution of Cretoceouj and older Tertiary rocks, and the 
Eocene River system. Lines A-A', B-B', and C-C show positions of cross sections shown on figure 3. 



1966 



DuRRFLL: Northern Sierra Nevada 



187 



The nature of the Cretaceous beds indicates that 
during their deposition the Sierra Nevada was a low- 
lying land contributing mud, sand, and pebbles to the 
adjacent sea. Presumabh- this was the condition at the 
beginning of the Tertiary, but there is no record dur- 
ing the long time span of Paleocene and lower Eocene. 

Eocene 
"Dry Creek" Formation 

The Upper Cretaceous beds at Pentz are overlain 
by gray shale and sandstone rich in biotite. The shale 
contains a marine fauna of middle Eocene age (Allen, 
1929, p. 367-369). Allen named the Eocene beds "Dry 
Creek"; that name was preempted but no new name 
has been assigned. According to Creely (1955) who 
reviewed the problem, the "Dry Creek" is 80 feet 
thick at the type locality. The area of exposure is 
quite small (fig. 1). 

lone Formation 

The lone Formation, which rests without angular 
discordance on the "Dry Creek" Formation at Pentz 
and elsewhere on the "bedrock series," is a group of 
continental sediments that crops out at intervals along 
the west base of the range as far south as Fresno 
County. It grades eastward into Eocene river gravels 
and sands. Westward it e.xtends into the Sacramento 
Valley subsurface where it rests on the marine lower 
Eocene Capay Shale. It is considered equivalent to 
the marine middle Eocene Domengine Formation, and 
is" overlain by the marine Markley Formation of upper 
Eocene age. 

The lone consists of claystone of various colors, 
mostly light shades, and of kaolinitic sandstones in 
which the sand grains are predominantly angular quartz. 
Much of the sandstone contains pearly flakes of kaolin, 
which Allen (1929) called anauxite. These flakes are 
to a considerable extent obviously pseudomorphs of 
biotite, although biotite itself is rare. The sandstones 
are white, red, orange, or mottled. They are usually 
not cemented, but are bonded with clay. Some glau- 
conite is present. In places there are lenses of quartz- 
rich gravel, and coal and lignite beds that are present 
have been mined locally. 

At Oroville Table Mountain the lone is 600 feet 
thick (Creely, 1955, p. 140), and at lone it is about 
1,000 feet thick (Allen, 1929). 

The lone is evidently a littoral-continental deposit 
that comprises a strip parallel to the length of the 
range. At South Oroville Table Mountain, just north 
of the city of Oroville (fig. 1), the lone on the west 
side is believed to grade into fluviatile "auriferous 
gravels" on the east side, a relationship agreed to by 
everyone who has studied the area. Allen (1929) cites 
abundant evidence from other areas to show the equiv- 
alence of the lone and the "auriferous gravels." At 
Oroville Table Mountain both units contain cobbles 
of hornblende andesite. 

Because the lone Formation rests in many places on 
the "bedrock series" deeply weathered to lithomarge. 



and because the lone itself is composed principally of 
quartz and clay, Allen believed that the lone sediments 
were derived under tropical or subtropical weathering 
conditions. 

"Auriferous gravels" 

The term "auriferous gravels" has been applied 
since early times to the ancient quartz-rich, gold-bear- 
ing stream deposits of the Sierra Nevada, once thought 
to be Miocene, but later recognized to be Eocene. 
Besides their physical equivalence to the lone, and of 
that to the Domengine Formation, the\' are inde- 
pendently dated paleobotanically (MacGinitie, 1941). 
Younger gold-bearing gravels are, of course, excluded 
from this category. Although the name is inappropri- 
ate because gold occurs in gravels of younger age, 
including the Recent, no one has yet suggested a 
better name. 

The "auriferous gravels" are in ancient river valleys 
and the river systems have been reconstructed in part 
(Lindgren, 1911) as shown on figure 1. The channels, 
in the valley bottoms, can be e.xamined in places where 
the gravel has been removed by hydraulic mining. 
Elsewhere the channels were explored by under- 
ground mining, and there is scarcely an\' portion of 
them that is unexploited. 

Most of the gold occurred in the lowest part of a 
channel where the gravel was generally bouldery, and 
composed mostly of local rock types. Above the gold- 
bearing sections the gravel is quartz rich, but not com- 
posed entirely of vein quartz, for chert and other 
quartz-rich rocks are abundant. At La Porte, for ex- 
ample, black, gray, white, and variegated chert unlike 
any yet discovered in the "bedrock series" of the 
Sierra Nevada is common, and it indicates a source 
east of the present limits of the range. Quartz-rich 
sand is abundant, and claystone and carbonaceous 
clays, no doubt deposited in ponds on flood plains, are 
present at La Porte. 

Lindgren (1911) believed that the rivers had their 
headwaters in the present Sierra Nevada, and he 
thought that he knew where the divide was between 
the coastal and the interior drainage as far back as 
the Cretaceous. His conclusion requires that all of the 
channel filling, including the gold, originated within 
the range as we now know it. However, the size of 
the channels in the present summit region and the 
occurrence of cobbles of rocks foreign to the Sierra 
Nevada indicate that the streams headed far to the 
east. Thus the Jura River that was supposed to flow 
northwestward across Sierra and Plumas Counties in 
the summit region could not have existed. Further- 
more, its course was dra\\n by linking occurrences of 
gravel of difi^erent ages and quite different petrologic 
characteristics. 

The plant remains contained in the "auriferous 
gravels" not only date them as Eocene or early Oligo- 
cene, but indicate that the climate of the region at 
that time was near-tropical, thus confirming the opin- 



188 



Gkology ok Norihi rn California 



Bull. 190 



ion of Allen (1929) with rcspccr to the lone Forma- 
tion. Potbury (19.?5) concliicicd that: "The distribu- 
tion of the modern relatives | of the fossil plants found 
at I-a Porte I indicates that the cliniate at I. a Porte dur- 
ing earl\- Tcrtiar\- w as intermediate betw een the tropi- 
cal climate of the w indward side of southern Mexico 
and Central .America and the warm temperate climate 
of the leeward side." .And, "An analy.sis of the leaf 
characters suggests that the flora occupied a position 
intermediate between a stricrl\ temperate and tropical 
environment." 

Gravels, composed mostl\' of mctavolcanic rocks 
and chert, and younger than the quartz-rich gravels 
also occur in Plumas County. Alany of the pebbles 
and cobbles arc like Sierra Nex'ada rocks and were 
no doubt of local origin, but man\' are not, and these 
must have been brought in from the east. These 
younger gravels occupv different channels than the 
quartz-rich gravels, although they overlap the latter 
in places. Mostl\- the\' are beneath the lavas of the 
Lovejoy Formation. They are unconformable on the 
older gravels and the "bedrock series." 

The headword extensions of these ancient rivers are 
either lost by erosion or concealed beneath younger 
rocks. 

Lovejoy Formation 

The Lovejoy Formation (Durrell, 19.'i9b) is re- 
stricted to the northernmost Sierra Nevada (fig. 1). 
It consists of a series of black olivine basalt lava flows 
that comprise a chain of outcrops extending across the 
region from the Hone\- Lake fault scarp above Hone\ 
Lake to Oroville Table Mountain. The same basalts 
are present in the Sacramento \'alley subsurface, and 
they crop out on the west side of the valley at Orland 
Buttes. The Putnam Peak Basalt near \'acaville is prob- 
ably the same series of flows. 

The several areas of occurrence across the Sierra 
Nevada are isolated from each other as a result of 
faulting and erosion, but there can be little doubt that 
they are remnants of a once continuous body. The 
occurrences are limited to a narrow belt across the 
region, and probably their original distribution was 
restricted in a similar v\a\', as b\' confinement to a 
broad shallow valley. 

The la\as of the Lovejoy Formation form flat- 
topped table lands with stepped sides. The cliffs usually 
extend through a single flow and benches mark the 
interflow contacts. As man>' as ten flows can be recog- 
nized in some sections. The maximum thickness is 
about 600 feet. The ground over the flows is stony, 
even in forest. Vegetation is usually sparse, and the 
poor soil is t\'pically chocolate colored. The rocks 
weather brown or dark gra\- and are dull black on 
fresh surfaces. A poorK- defined columnar structure 
is present in most places and joints are closcl\' spaced. 
\'^esicles, sparse in most flows but abundant in a few, 
usually show no flattening due to flow. An orientation 
of feldspar microlitcs is present in some flows and is 



evidenced by a sheen on the surface. Scoria zones are 
absent betw een flow s, and even in good exposures the 
interflow contacts are diflicult to locate. Sand and 
gravel in small amounts occur locallv between flows. 

The unusual microscopic textures of the lavas have 
been discussed in detail by Durrell (19.^9b), and are 
the principal basis for correlation of the many isolated 
occurrences of the lavas. 

The Lovejoy Formation rests unconformably on 
either the "auriferous gravels," the lone Formation, or 
the "bedrock .series." 

No local sources of the ba.salts have been identified; 
hence they are believed to have originated east of the 
Honc\- Lake fault scarp. Pebbles and cobbles betw een 
flow s include hornblende andesite, and granitoid rocks 
unlike those of the northern Sierra Nevada, which, 
therefore, indicate an eastern source. 

The Lovejoy Formation has been dated b\- J^urrell 
(19.>9b) from relationships at La Porte, where in the 
Upper Ditch Diggings of the La Porte hydraulic pit 
there are two immense boulders of Lovejoy Basalt 
and numerous smaller pieces. Small pieces are also 
present in lacustrine clays that overlie the gold-bearing 
gravels. Above the clays is the La Porte tuff which 
contains a flora dated as latest Eocene or early Oligo- 
cene (Potbury, 1935). Thus the Lovejoy is older than 
the La Porte flora and could be latest Eocene or early 
Oligocene also. The Lovejoy lies unconformably 
below the Ingalls Formation, which is believed to be 
Oligocene, and that in turn is unconformably below 
the Delleker Formation w hich is probabi)' lower .Mio- 
cene. 

On the other hand, Dalrymple ( 1964) considers the 
Lovejoy to be earh- Miocene b\- radiometric methods. 
Whole rock determinations of Lovejoy basalts give 
dates of not more than 13.6 million years which arc 
considered invalid. A date of 23.8 million years ob- 
tained on plagioclase from a tuff bed below the Love- 
jov at Oroville Table .Mountain is considered valid. 
For this reason Dalr\mple believes the Lovejo>- to be 
younger than that, in spite of the fact that this date is 
also >ounger than some he obtained from the Delleker 
Formation (20.5 to 26.1 million years) which rests 
unconformabl)' on both the Lovejo\- and Ingalls For- 
mations. Dalr\-mple explains away the relations at La 
Porte on grounds that he was unable to find the clasts 
of Lovejoy basalt in place in the clays below the La 
Porte tuff. 

Oligocene 
Wheatland Formation 

The Wheatland Fomiation (Clark and Anderson, 
1938) crops out in a small area along Dr\- Creek 6 
miles northwest of the town of Wheatland at the west 
base of the mountains (fig. 1). The occurrence is sur- 
rounded b\' alluvium. The beds are about 300 feet 
thick and dip 3° to 5^ to the .southwe.st. They consist 
of shale, sandstone, and conglomerate containing peb- 
bles of granitoid and mctamorphic rock, hornblende 



1966 



DuRUF.LL: North i-.RN Sif.rra Nkvada 



189 



andesite, and olivine basalt. A marine invertebrate 
fauna described by Clark (Clark and Anderson, 193S) 
is determined to be lowest Oligocene or upper 
Eocene, and is considered by Weaver et al. (1944) to 
be lowest Oligocene. A radiometric age b\' Dalrymple 
(1964) of andesite pebbles from the Wheatland is 53.5 
million years. 

Reeds Creek Andesite 

A few miles north of the Wheatland Formation 
along Reeds Creek there crops out a series of andesite 
mudflow breccias and conglomerates that rests on the 
lone Formation and overlaps the "bedrock series", 
named the Reeds Creek Andesite by Clark and Ander- 
son (1938). This is in turn overlain by rhyolite tuff, 
which is probably a correlative of either the Delleker 
Formation or the \'alle\- Springs Formation of the 
central Sierra Nevada, but the contact between the 
two is concealed by a strip of alluvium three-fourths 
of a mile wide. Clark and Anderson suggest that the 
Reeds Creek might be the source of the hornblende 
andesite pebbles in the Wheatland Formation, and 
that it might, therefore, be Eocene. It is not realh- 
certain whether the Reeds Creek is older or younger 
than the Wheatland for no fossils have been found 



Ingalts Formation 

The Ingalls Formation (Durrell, 1959a) consists of 
andesite mudflow breccia, which is virtually unbedded 
except localh' at the base \\here conglomerate occurs. 
The mudflows and the clasts in them are dark colored, 
and mostly of pyroxene andesite, but with some horn- 
blende andesite in which the hornblende phenocrysts 
are large in size but small in amount. Quartz diorite 
blocks of local origin are present in the lower part, 
and clasts of the Lovejoy Formation basalts have been 
found in the breccia. The Ingalls rocks characteris- 
ticalh' form prominent black craggy outcrops. 

The Ingalls is separated from both older and younger 
rocks by unconformities. It rests variously on "auri- 
ferous gravels," the Lovejoy Formation, and on the 
"bedrock series." It lies across fault contacts between 
older rocks, hence is separated from them by an epi- 
sode of faulting and erosion. Because its upper surface 
is also an unconformity, its original thickness is un- 
known. The present maximum thickness is 550 feet. 

The Ingalls is present in the Diamond and Grizzly 
Mountains and in the Plumas Trench between the 
Grizzly .Mountains and the Sierra Nevada. It has not 
been identified in the Sierra Nevada proper. 

The age of the Ingalls has not been closely estab- 
lished. It is \ounger than the Lovejoy Formation, but 
is older than the superimposed Delleker Formation 
which appears tp be early Miocene. The Ingalls is pos- 
sibl>' correlative with the Aha Andesite at \^irginia 
City, Nevada, which contains the Oligocene Sutro 
Tuff Member (Gianella, 1936), and with the Wheat- 
land Formation, also Oligocene. 



The Aliocene Delleker and Bonta Formations and 
their equivalents together with the Pliocene Penman 
Formation and the Warner Basalt and their equivalents 
are shown as a single unit in figure 2. West of the 
crest of the Sierra Ne\ada these rocks are confined 
to the interstream ridges, and the irregular pattern of 
occurrence is owing to erosion. The rocks are more 
extensively' preserved cast of the crest owing to their 
structurally lower position. 

Dellelier Formation and Its Probable Equivalents 

Rh\olite tuff is widely distributed in the northern 
Sierra Nevada but has been assigned a formation name 
onl\' in Plumas Count\- where it was named Delleker 
by Durrell ( 1959a). It is not clear whether the Delle- 
ker and the Valley Springs Formation of the central 
Sierra Nevada, also rh\'olite tuff, are equivalent. 

The rhyolitic deposits consist of welded tuff, or 
ignimbrite, especially in the east, water-lain ash and 
volcanic mud, and quartz-sand and gravel. Most of 
the tuff is white or cream colored, but some of the 
ignimbrite is tan, brown, and pink. Quartz, sanidine, 
and biotite are usuall\- conspicuous. 

Sand and gravel beds are common especially at or 
near the base, but in many places pebbles and cobbles 
are found distributed through the tuff. In Placer 
County, along Highway 40 (Interstate 80) the quartz- 
sand and gravel is undoubtedl\- reworked from the 
older "auriferous gravels." In Plumas County, gravels 
at the base of the Delleker are auriferous and contain 
granoph\Tic granite and metaquartzite that are foreign 
to the Sierra Nevada and indicate an eastern source. 

The rhyolite tuff was no doubt deposited as a sheet 
over the region, but it is now discontinuous and pres- 
ent often in only very small areas. This distribution 
is owing both to erosion alone, which isolated the 
lowest parts of the formation, and to faulting and 
erosion as is clearly the case in the Grizzh' and Dia- 
mond Mountains. 

The rhyolite tuff beds are usually less than 400 feet 
thick, but equivalent beds farther east are ver>- much 
thicker, as for example, in the \'irginia Range west 
of Pyramid Lake, Nevada, where they are 3,500 feet 
thick (Mcjannet, 1957). 

No sources of rhyolite tuff are know n in the north- 
ern Sierra Nevada, and the>- undoubtedly lie farther 
east. Tuff flows hot enough to w eld reached the east- 
ern part of the range, but only water-lain tuff is pres- 
ent farther west. 

The age of the Delleker Formation in Plumas 
County is established only indirectly by paleontologic 
means. In the \'irginia Range, west of Pyramid Lake, 
Nevada, the equivalent of the Delleker is overlain by 
a diatomite that contains fossil leaves dated as middle 
Miocene (D. I. Axelrod in Mcjannet, 1957). Hence 
the Delleker is probably middle or lower Miocene, or 
possibly even Oligocene. Radiometric ages on samples 
from Plumas County (Dalrymple, 1964) range from 



190 



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1966 



DURRF.I 



NoRTHKRN Slr.RRA NkVADA 



191 



20.5 to 29.9 million years, based on potassium-argon 
ratios in sanidine and biotite. Because of possible con- 
tamination of the biotite with biotite reworked from 
Mesozoic plutonic rocks, the older dates are consid- 
ered unreliable. The ages based on sanidine range from 
20.5 to 26.1 million years, or early Miocene, according 
to Dalrymple (1964). Determinations on sanidine from 
the ignimbrites at Donner Pass on Highway 40 give 
values of 33.2 and 26.0 million \ears, which Dalrymple 
assigns to late Oligocene and early Miocene, being 
roughly in agreement with the radiometric age of the 
Delleker Formation in Plumas County. 

Bonta Formation 

The Bonta Formation is widespread in eastern 
Plumas County in the Grizzly and Diamond Moun- 
tains and in the Mohawk \'alley. So far it has been 
recognized in the Sierra Nevada proper only at Gold 
Lake in Sierra Count\% where recent road construc- 
tion exposed a thin fossiliferous section previously en- 
tirely concealed by glacial deposits. 

The Bonta consists mostly of volcanic conglomerate 
but includes some mudflow breccia. The conglomerate 
is mostly of pyroxene and hornblende andesite blocks, 
cobbles, and boulders, some of which are surely re- 
worked from the Ingalls Formation. Rhyolitic debris 
reworked from the Delleker Formation ranging from 
single clear crystals of quartz and sanidine to blocks 
and boulders of ignimbrite 4 feet in diameter are 
w idely present. Phases of the Delleker not known to 
occur any place farther west than Red Rock Canyon 
on the California-Nevada boundary- are found in the 
Bonta 30 miles west of there. 

Boulders of quartz diorite of local origin, some as 
much as 20 feet in diameter are common and con- 
spicuous, and are found many hundreds of feet above 
the base of the formation. Consideration of the geol- 
ogy of the "bedrock series" indicates transportation 
in a westerly or southwesterly direction. In the Dia- 
mond Mountains the Bonta Formation contains gra- 
nitic debris and feldspar fragments, probably from peg- 
matites, that are not known any place west of the 
Honey Lake fault scarp. Grains of quartz, biotite, and 
feldspar from granitoid sources are present every- 
where in the Bonta. The mudflow breccias are of 
hornblende andesite in which the hornblende pheno- 
crysts are rather large and few in number. The rock 
fragments are predominantly dark colored. These fea- 
tures serve to distinguish the Bonta from the younger 
Penman Formation. 

The Bonta rests unconformably on the Delleker, the 
Ingalls, the Lovejoy, and the "bedrock series." Fault- 
ing preceded the episode of erosion expressed by the 
unconformity. The maximum known thickness of the 
Bonta is about 1,000 feet. 

The age of the Bonta is established as upper Mio- 
cene by the fossil leaves of the so-called Mohawk 
flora found at its base near Clio, California. The flora 
was first described by Knowlton (Turner, 1891, 1895) 



and assigned to the Miocene. Axelrod (1957) referred 
the age to upper Miocene. The recently discovered 
flora at Gold Lake is the same age (D.I. .\xelrod per- 
sonal communication). 

The well-exposed section of andesite mudflow brec- 
cia and conglomerate 1 mile east of Emigrant Gap on 
Highway 40, is very much like the Bonta Formation, 
but it is not dated. 

The source of much of the material comprising the 
Bonta Formation is known, but much, especiall>' the 
mudflow breccia, has unknown sources. Hornblende 
andesite intrusions in the Sierra Nevada, Grizzly, and 
Diamond Mountains resemble more the younger Pen- 
man Formation; none are considered to be sources of 
the Bonta. 

Pliocene 
Penman Formation and Its Probable Equivalents 

The Penman Formation (Durrell, 1959a) consists of 
volcanic mudflow breccia, with lesser amounts of con- 
glomerate, fanglomerate, mudstone, sandstone, tuff, 
and lavas, dominantly of hornblende andesite, and 
with relatively little nonvolcanic material. 

The andesites are light colored, with very abundant, 
small phenocr\'sts of hornblende. The induration of 
the clastic rocks is much less than that of older units. 

In the Grizzly ^Mountains, which contain the t>pe 
area, and in the Diamond Mountains the deposition of 
the Penman was preceded by an episode of faulting 
and erosion. The Penman consequently rests on all of 
the older rocks in one place or another. It extends into 
the Sierra Nevada proper, and, w ith minor exceptions 
already noted, all of the hornblende andesite north of 
the North Fork of the Yuba River that has been re- 
cently examined is Penman Formation. Andesitic rocks 
south of the North Fork of the Yuba have not been 
studied in recent years. 

The Penman Formation as established in the Grizzly 
Mountains cannot be closely dated. It is unconform- 
able on the Bonta, which is upper Miocene at its base. 
It is older than the Warner Basalt which is believed to 
be middle or upper Pliocene. Hence, the Penman is 
probably lower or middle Pliocene or both. 

At Remington Hill, in the Yuba River basin, andes- 
sitic rocks contain fossil leaves which have been as- 
signed to the Mio-Pliocene by Condit (1944), and cor- 
related with the .Mio-Pliocene Mehrten Formation of 
the central Sierra Nevada. 

The relationship of the Penman to the Mehrten For- 
mation of the central Sierra Nevada is not clear, but it 
is possible that the Mehrten is equivalent to the Pen- 
man and Bonta together. 

The maximum thickness of the Penman in the Griz- 
zly .Mountains is 1,350 feet, which is less than the 
original thickness by an unknow n amount because of 
erosion. In the Sierra Nevada proper, the Penman and 
its probable equivalents farther south are about a thou- 
sand feet thick in the summit region, and 200 to 400 
feet thick at the edge of the Great \'alley. There is a 



192 



ClOI.OdV ()!• NoRTHIRN C.M.I lOKM \ 



Hull. 190 



rough gradntion from coarse to Hue toward the west. 
In Pluinas County there is some evidence of westerlx' 
transport across the present summit region of the 
Sierra Nevada. 

The Penman is presumed to ha\c had many local 
sources both in the summit region of the Sierra Ne- 
\ada and farther cast. Plugs of hornblende andesite as 
much as a mile in diameter and many lesser intrusions 
are alnindant. The problem of the origin of the breccia 
structures is discussed more fully in a later section of 
this report. 

Worner Basalt 

The Warner I?asalt consists of lava flows of prc- 
dominatiy light-gra\' olivine basalt \\ ith conspicuous, 
abundant, small phenocrysts of yellow or golden oli- 
vine. (]reen augite piienocrysts are present in some 
rocks. Dikt\ta.\itic texture is characteristic but is not 
present in all flows. Where the "bedrock series" is 
granitoid the basalt is often contaminated. Such rocks 
commonly lack olivine, and usualh' contain obvious 
.xenocrysts from the granitoid rocks. 

Platy jointing is pronounced and columnar jointing 
is uncommon. Individual flows are usually thin, vesic- 
ular structure is common, and scoriaceous zones 
occur. 

The thickness of the Warner varies depending on 
the amount of erosion that it has suffered. It is 1,000 
feet thick at Thompson Peak in the Diamond Moun- 
tains, 350 feet thick in the Grizzl\' Mountains, and less 
than that in the Sierra Nevada in Sierra County. No 
clastic material and no fossils are know n to be asso- 
ciated with these rocks. 

The Warner was deposited as a sheet over the re- 
gion of the Diamond Mountains and Grizzh' Moun- 
tains, and a part of the northern Sierra Nevada proper, 
with flows undoubtcdl}' originating localh' from the 
numerous plugs of the same rock scattered over the 
area. No traces of volcanoes remain in this region ex- 
cept po.ssibly for Mount Ingalls in the Diamond Moun- 
tains. 

The flows were extruded onto an erosional surface 
that cut deeply into all the older formations so that in 
various places it rests upon Penman, Bonta, Ingalls, 
Lovejoy, and the "bedrock series." 

The name Warner was first applied by R. J. Russell 
(1928) in the Warner Range of far northeastern Cali- 
fornia, and was extended by Durrcll (1959a) to the 
Sierran region. The age is considered provisionall\- to 
be upper Pliocene because of its apparent relation to 
the Tuscan Formation of the region just north of the 
Sierra Nevada (Durrcll, 1959a). 

Similar rocks near Lake Tahoe and Truckee are 
as.sociatcd with cinder cones and are believed younger 
than the Warner farther north (Birkeland, 1963). 

The Warner Basalt was the last unit to be deposited 
across the northeastern part of this region, and its 
deposition was followed by the episode of faulting that 
lifted the Sierra Nevada to its present height, produced 



the Grizzly and Diamond Mountain blocks, and finally 
terminated drainage across the Sierra Nevada from 
w hat is now the Great Basin. 

Plio-Plelstocene Lacustrine Deposits 

The episode of post-Warner faulting mentioned 
above created a number of basins that held lakes, all 
of which became filled with sediments, or had their 
waters drained, before modern times. Lakes existed in 
.Martis, Sierra, Mohawk, Long, Spring Garden, .\meri- 
can Grizzl\-, Clover, and Indian \'alleys, and in the 
basins now occupied by the reservoirs of Lake Al- 
manor and Mountain .Meadows (figs. 1 and 2). 

Of all these basins only Martis V'alley and Mohawk 
\'allc\ have been dissected, and thev alone have re- 
ceived recent study. 

The Mohawk Lake beds are localized in a T-shaped 
basin with the 14-mile-Iong head at the base of the 
Sierra Nevada, and the 7-niile-long stem extending 
northeastward. The lacustrine sediments are boulder 
and pebble conglomerate, sandstone, shale, and lignite. 
The carbonaceous sediments are localized in the cen- 
tral part of the basin. All sedimentar\- materials are 
of local origin. The exposed thickness of beds is 400 
feet, and another unexposed 400 feet is known because 
of wells in the center of the basin. The total thickness 
is unknown. 

The lake floor terrace is well preserved in man\' 
places, and the shoreline la\- between 5,000 and 5,050 
feet elevation. The basin probably still contained wa- 
ter to a depth of 200 feet when it was drained by 
capture. Small faults cut the lake beds, but there h;ii> 
been no large-scale deformation. 

.\ till sheet is interbedded with the lake sediments 
along part of the south side of the basin, and great 
moraines rest on the lake terrace; hence most of the 
basin fill is preglacial. A pollen flora from carbona- 
ceous beds at the low-est exposed level shows a forest 
like that present in the region toda\- (D. I. Axelrod, 
oral communication). 

Pleistocene and Recent 
Glacial Deposits 

Four glaciations have recently- been recognized in 
the region between the north end of Lake Tahoe and 
I'ruckcc and extending north of Highw a\- 40 for some 
distance (Birkeland, 1964). The corresponding depos- 
its are described in the same work. 

.\t least four stages of glaciation are visible on 
casual examination of the divide lietween the North 
Fork of the Yuba River and the Middle Fork of the 
Feather, but no detailed studies have been made. The 
earliest is represented by the till sheet in the Mohawk 
Lake beds south of Blairsden. Lateral moraines as 
much as 3 miles long extend out onto the Mohawk 
Lake terrace along Jamison, Grav F.agle, and Frazier 
Creeks. Lesser glacial .stages are represented at higher 
levels. Glacial lake basins resulted both from deposi- 
tion and erosion, and some of them later became filled 



1966 



DUURKI.I.: NoRIHKRN SiFRRA Nl.X'ADA 



193 



with sediment. The town of Johnsviile is situated on 
a terrace resulting from the filling of a moraine- 
dammed lake that has been dissected consequent on 
the drainage of the slightly lower Mohawk Lake. 

Minor glacial deposits occur elsewhere in the higher 
parts of the region including the Grizzly Mountains 
and Mount Ingalls. 

Terrace Deposits 

Terrace deposits are minor but occur sparingly 
along the southwest-flowing streams. All were mined 
for gold in the early days of the gold rush. Terraces 
occur in Mohawk Valley and seem to have been 
caused by a short-lived landslide dam on the Middle 
Fork of the Feather River. 



The Region is undergoing erosion so that, with the 
exception of the lacustrine deposits already described, 
alluvial deposits are only narrow strips of coarse clas- 
tic sediments along the stream courses. 

GEOLOGIC STRUCTURE 

The Sierra Nevada proper is a nearly monolithic 
block tilted westward by uplift along a fault system 
at its eastern limit. The simple fault block concept 
must be qualified, however, because faults that cut 
rocks as young as Pliocene are present within the 
block, although most have small displacements. Their 
presence was early recognized by Whitney (18S0) in 
the La Porte-Gibsonville area. Because of their small 
displacement, and because they were observed during 
underground mining of the "auriferous gravels" and 
their location is therefore now uncertain, they are not 
shown on section A- A' of figure 3. 

Faults within the range are apparently more closely 
spaced near the crest (sec. B-B', fig. 3). Not all faults 
affect the youngest rocks, and such is the case on 
Boreal Ridge, a mile northwest of Donner Pass ( Hud- 
son, 1951), where basalts dated as Pliocene (7.4 mil- 
lion years) by Dalrymple (1964) are not cut by faults 
that cut . older Tertiary. No one has yet detected 
within the range Eocene to Miocene episodes of fault- 
ing, yet it is clear that deformation did occur for the 
several stratigraphic units of that age are separated by 
unconformities. 

In contrast to the apparently simple structural his- 
tory of this block, the region immediately to the east 
has had a long and complex history. The east front of 
the Sierra Nevada northwestward from Donner Pass 
is a complex zone of faulting. It has not been studied 
in detail except at Donner Pass (Hudson, 1948, 195.'i) 
and in the Blairsden quadrangle and vicinity in Plumas 
County (Durrell, 1959a, 1965). Northeast of the Sierra 
Nevada proper, in the Grizzly and Diamond Moun- 
tains, the Lovejoy, Ingalls, Delleker, Bonta, and Pen- 
man Formations, and the Warner Basalt and Mohawk 
Lake beds are each separated from the previous unit 
by a period of faulting and erosion. All beds are still 



essentially horizontal. The pattern of faulting and ero- 
sion was such that each unit rests at one place or 
another on each older unit including the "bedrock 
series." This is illustrated in part in section C-C of 
figure 3. There it is seen that the "auriferous gravels," 
Lovejoy, Bonta, and Penman Formations rest on the 
"bedrock series," and the Bonta rests also on "aurif- 
erous gravels" and on the Lovejoy Formation. Nearb\', 
though not on the line of section, the Bonta occurs 
in its normal position on the Delleker Formation. The 
Penman rests also on the Bonta Formation in section 
C-C and elsewhere, but nearby it rests on Delleker 
and Ingalls. The Warner is present in section C-C 
only in its normal position above Penman, but at (jold 
Lake in the Sierra Nevada it rests on the "bedrock 
series"; about a mile southeast of the midpoint of 
section C-C it rests on Bonta, and 5 miles north of 
the northeast end of the section it rests on both Ingalls 
and Lovejoy. 

.Most faults are apparentl\- normal, but not all can 
be so categorized since a good many show reversal of 
movement (fig. 4). The fault surfaces generall\- dip 
steeply, and no doubt some are vertical or nearl\- so. 

Between the Sierra Nevada and the Grizzh' Moun- 
tains is a graben comprising a lowland called the 
Plumas Trench which contains Mohawk, Long, Spring 
Garden, and American X'alleys (fig. 1 and 2). The 
boundary faults are normal, that is, they dip toward 
the graben at 55° to 75°. However, the major fault 
on the southwest side of the graben has a left-lateral 
separation of 3 Vz miles (Durrell, 1950, 1965). There 
is evidence that suggests left-lateral separation of as 
much as 8 to 9 miles on the northeast boundary- fault. 
The date of the lateral components of motion on these 
faults is uncertain. 

A pronounced change in the Tertiary' stratigraphic 
section takes place along the northeast side of the 
graben — that is to say, the section in the graben is 
more like that of the Sierra Nevada proper than that 
of the Grizzly Mountains. The Ingalls Formation is 
absent, the Bonta is ,scarcel\- represented, and the other 
units are generalh' thinner on the southwest. Thus it 
is evident that the Sierra Nevada block tended to be 
high relative to the land to the northeast, and this was 
evidently accomplished by slip on the northeast side 
of the present graben. If the uplift occurred on the 
fault or faults that now bound the graben on its north- 
east margin, then the movement was reverse and the 
forces were probably compressional. In late Pliocene 
or early Pleistocene w hen the Sierra Nevada w as ele- 
vated and drainage s\stems from the interior were 
finally disconnected, the movement on the previously 
active reverse fault was reversed and ultimately be- 
came larger in amount so that present .stratigraphic 
separations indicate only nomial faulting. 

The more recent fault movements produced the ex- 
isting major landscape features: the Sierra Nevada; 
the adjacent lowlands such as Martis Valley, Sierra 
\'alley, and the Plumas Trench; the Grizzly Moun- 



194 



Geology of Northf.rn California 



Bull. 190 



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1966 



DuRRKi.L: North (•RN Sif.rra Nkvada 



195 



SEC 29 SEC 2B 




CONTOUR INTERVAL 50 FEET 



Geology tiy 
EXPLANATION Cordell OurrsM 



Upper . 
p I i ocene I 



Midd le 
P I i Dcenel 



Upper(?)J 
Ml ocene 



MIdd le 
Mi ocene (? )| 



01 i gocene ( ? )-< 



Olive base 1 1 
Intrusive: 



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Mb 

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Bont a For«a t I on 




De I I eke r For ma t I on 



$1 



Inga I Is Forma t i on 



~.X . .\NNv 



Love joy Forma t i on 

Figure 4. Geologic map of a small portion of the Blairsden quad- 
rangle, Plumas County, California, showing reversal of fault movement. 

tains, Grizzly \'ailey, the Diamond Mountains, and 
the Honey Lake Basin. 

Fault displacements at this time \\ ithin these major 
structural units were probably small, but erosion has 
cut so deeply that the Warner Basalt, the youngest 
unit afFected, has been largely removed, making it 
difficult to determine the amount of movement. 

The magnitudes of net separations vary greatly. In 
the Sierra Nevada proper, as between La Porte and 



Gibsonville, the>' range from a few feet to a few tens 
of feet. Toward the eastern limit of the Sierra Nevada 
proper as shown in Section B-B' of figure 3, vertical 
separations are as much as 300 feet. The main fault 
between the Sierra Nevada and the Plumas Trench 
has a vertical separation at the base of the Penman 
Formation of 2,500 to 3,000 feet in the vicinity of 
Section C-C of figure 3. Farther southeast where the 
Penman is concealed beneath the Mohawk Lake beds, 
the vertical separation could be more than 4,000 feet. 
Vertical separations along the northeast side of the 
Plumas Trench arc more difficult to determine, but 
they exceed 1,000 feet in many places and probably 
exceed 2,000 feet in others. 

In the Grizzly and Diamond .Mountains the pattern 
of faulting is exceedingly complex with many in- 
stances of reversal of movement (fig. 4). Most vertical 
separations are of the order of a few hundred feet. 
It would be good to know the absolute elevation 
changes connected w ith faulting, but this has not yet 
been determined b\- ph\sical methods in spite of some 
valiant attempts by Lindgren and Hudson (1955, 
I960). The best information is paleobotanical in nature 
and the best data are contained in the writings of 
D. I. Axelrod. 

Clearl\-, from middle Eocene through early Oligo- 
cene the region had a near-tropical climate (Allen, 
1929; Potbur\', 1935), and was probably not far above 
sea level. By upper Miocene, \\ hen the lower part of 
the Bonta Formation was deposited the land was still 
low, but the climate was much more temperate. The 
fossil flora (iMohawk flora) at Clio in the .Mohawk 
Valley, at an elevation of 4,450, is the same as that 
at Gold Lake at an elevation of 6,600 feet. Both were 
deposited at an elevation of not more than 2,000 feet 
above sea level (Axelrod, 1962). Since the Mohawk 
Lake beds of latest Pliocene or early Pleistocene con- 
tain a pollen flora like that of the present forest, it 
appears that the net uplift of the northern Sierra Ne- 
vada between upper .Miocene and early Pleistocene 
was more than 4,000 feet. This must have occurred 
entirely in post-Penman time, and possibly entirely 
in post- Warner time. 

The elevation of the Sierra Nevada culminated in 
glaciation, already described. Sufficient elevation oc- 
curred to permit minor glaciation on the north slopes 
of the highest parts of the Grizzl>' and Diamond 
Mountains. 



.Man\' problems in sedimentar}- and in igneous pe- 
trology, and man\- that are combinations of the two, 
await stud\'. 

It is now 35 years since Allen (1929) published his 
superb monograph on the lone Formation and the 
\\ eathered zone that underlies it, and although his main 
conclusions are not likely to be changed it is possible 
that refined interpretations could come from a study 
based on the newer techniques of petrology. 



196 



Cil'()I.(K;V OK NoRllllRN Cm.IIORMA 



Bull. 190 



The "auriferous giiucls" ha\c never been stuciieci 
petrographicail\- except by students whose disserta- 
tions remain unpublished. In order to understand the 
sources of mineral and rock constituents, we must have 
a much better know ledge of the petrography of the 
"bedrock series" than we have at present. Some slight 
progress has been made in Plumas Count\- as is indi- 
cated above. The courses of the streams that deposited 
the gravels are subject to reinterpretation through 
modern approaches to petrology, stratigraph\-, and 
structure. 

The I.ovej<)>- Formation presents a puzzling prob- 
lem in regard to the source of lava. No sources have 
been recognized an\where, >ct if the source lies con- 
cealed east of the Honey Lake fault scarp, the required 
distance of flow seems unreasonablx- long. No attempt 
has _\et been made to correlate individual flows from 
outcrop to outcrop. If this could be accomplished it 
would ccrtainl\- shed light on the source problem. 

Although some intrusions of rhyolite have been 
descril)ed from the summit region of the central Sierra 
Nevada (Curtis, 1954), the rh\olitc tuffs and ignim- 
brites mostly had sources east of the Sierra Nevada. 
The\- are a part of the enormous mass of rh\()litic 
erupti\e material of mid-Tertiary age that extends 
throughout the Great Basin. Correlation of tuff beds 
and ignimbrites from one area of ocurrence to another 
is a difficult problem in the absence of fo.ssils; the ra- 
diometric data seems yet to be insufficiently sensitive, 
hence the uncertaint\- about the relation of the Delle- 
ker to the \'alle\' Springs I'ormation. It is not clear 
how man\' episodes of rhyolitic eruption occurred. 

The Warner Basalt presents some interesting prob- 
lems resulting from its contamination b\- silicic material 
that are awaiting studw The Warner is also part of a 
large problem, for that part in the northern Sierra 
Nevada is but the southernmost portion of a flood of 
olivine basalt that covers an enormous area in north- 
eastern California, northwestern Nevada, and Oregon. 

Perhaps the most fascinating petrologic problem 
concerns the origin of the andesite intrusive breccias 
and the andesite mudflow breccias that comprise by 
far the greater part of all the Tertiary deposits of the 
region. The mudflow breccias puzzled the older 
workers, and they remain a puzzle. Turner (1S95, 
1896) was probably the first person to consider their 
origin. He pointed out that they are in fact mudflow 
deposits and not ordinary pyroclastic rocks. Lindgrcn 
(1H97) also described them and noted that they orig- 
inated from sources along the crest of the range. 

Anderson (193 3) thoroughl\' reviewed the mudflow 
problem in connection with his stud\ of the Tuscan 
Formation, which is w idespread immediatel\' adjacent 
to this region on the north. He concluded that mud- 
flows could travel far enough to account for the dis- 
tribution of the Tuscan Formation — about 50 miles 
(a comparable distance would apply to the Sierra 
Nevada) — and that they could move on slopes such as 
seem to have existed when the Tuscan was deposited. 



He thought that melting snow and ice could provide 
the water, and he discussed the capability of mudflows 
to transport ver_\- large blocks of rock. However, it is 
not clear what he thought was the cause of the brecci- 
ation. 

In 1944 Durrell described eight dikes of andesite 
breccia that intrude andesite mudflow breccia, tuff, 
and a brecciatcd andesite lava flow near Blairsden. In 
this lava flow, w hich is flow banded, the brecciation 
process has not disturbed the attitude of the flow band- 
ing, which is in parallel position in all blocks even 
where separated b\' several feet of comminuted ande- 
site indistinguishable from the finer parts of the intru- 
sive breccias. Durrell concluded that the dikes and the 
lava flows were brecciated by the same process, which 
he thought due to increasing vapor pressure of water 
dissolved in the glass of the cooling rock. 

He expres.sed the view that generalh' brecciation 
took place before the magma reached the surface, but 
that in some instances it was dela\ed until after ex- 
trusion; that the water vapor that caused the breccia- 
tion altered the glass to cla\-; that the water then con- 
densed to form a mud matrix; and that the extruded 
product was a breccia with a mud matrix. .Motion due 
to the intrusive impulse or due to gravit\- seemed un- 
necessary to account for the brecciation. 

In 1954, G. H. Curtis published an important paper 
on the origin of the andesite breccias of the Sierra 
Nevada; he expressed a different interpretation based 
on observations on the mudflow breccias and on many 
intrusive breccias and brecciated lava flows like those 
previously described b\- Durrell. Notable new obser- 
vations were that some of the dikes have massive un- 
brecciated selvages and that some of the brecciated 
lava flows are massive at the base. 

Curtis again reviewed the problem of the origin of 
volcanic mudflows. In his view the andesite magmas 
have a low water content; the initial stages of breccia- 
tion of both the lava flow s and the dikes is due to the 
escape of the small amount of fluids, and the major 
part of the brecciation is due to motion of the nearl\' 
congealed magma, although he recognized that some 
of the breccias give evidence of onl\- ver\- slight 
motion. 

In Curtis' opinion, mudflows resulted from the mix- 
ing of the water of rivers, lakes, and rain with the 
extruded breccia. He had nothing to say about the 
formation of clay or its role as a lubricant in the ex- 
trusion process, or on the matter of the slopes neces- 
sar\- to initiate flows of volcanic breccia that have 
traveled more than 50 miles. 

Clearlv the problem of the brecciated lava flows, 
dikes, and mudflow breccias is not yet solved. Some 
salient facts that must be accounted for are the follow- 
ing: The amount of extrusive breccia is very large. 
Durrell once estimated it to be between 1,100 and 1,300 
cubic miles, and Curtis (1954) estimated it to be 2,000 
cubic miles. Lava flows including brecciated flows 
comprise a minute proportion of the total. The slope 



1966 



Duiuu, 



NORIHKRN SiKRRA Nl-.VADA 



197 



over which the mudflows traveled was very gentle, as 
paleobotanic evidence indicates that the elevation of 
the present summit region \\as not more than 2,000 
feet. Since the western edge could not have been lower 
than at present, the slope averaged 1:130. Certainh- 
portions of the summit regions may have exceeded 
2,000 feet in height, but no great chain of high vol- 
canoes like those of the Cascade Mountains existed 
here in late Miocene or Pliocene time. Although most 
of the breccia is late Miocene and Pliocene in age, 
there are similar rocks of Oligocene age, so that the 



process of mudflow formation extended through a 
major portion of the Tertiar\'. The brecciated lava 
flows and some of the breccia dikes and plugs give 
cx'idence that brecciation can occur without a signifi- 
cant amount of motion, that is, without translation 
or rotation of blocks from the prebrecciation position. 
Clay is a significant part of the brecciated lavas and 
intrusions, and is also the binder of the mudflow brec- 
cias. These facts indicate that the cause or causes of 
brecciation are not surficial accidents but are in some 
way related to the nature f)f the magma. 



REFERENCES 



Allen, V. T., 1929, The lone formation of California: California Univ., 

Dept. Geol. Sci. Bull., v. 18, no. 14, p. 347-448. 
Anderson, C. A., 1933, The Tuscan formation of northern California, 

with a discussion concerning the origin of volcanic breccias; Cali- 
fornia Univ., Dept. Geol. Sci. Bull., v. 23, no. 7, p. 215-276. 
Axelrod, D. I., 1957, Late Tertiary floras and the Sierra Nevada 

uplift [California-Nevado]: Geol. Soc. America Bull., v. 68, no. 1, 

p. 19-45. 
1962, Post-Pliocene uplift of the Sierra Nevada, California: Geol. 

Soc. America Bull., v. 73, no. 2, p. 183-198. 
Birkeland, P. W., 1963, Pleistocene volconism and deformation of the 

Truckee area, north of Lake Tahoe, California: Geol. Soc. America 

Bull., V. 74, no. 12, p. 1453-1464. 
1964, Pleistocene glaciotion of the northern Sierra Nevada, north 

of Lake Tahoe, California: Jour. Geology, v. 72, no. 6, p. 810-824. 
Clark, B. L., and Anderson, C. A., 1938, Wheatland formation and its 

relation to early Tertiary andesites in the Sierra Nevada; Geol. Soc. 

America Bull., v. 49, no. 6, p. 931-956. 
Condit, Carlton, 1944, The Remington Hill flora [California], Chap. 2 

of Choney, R. W., ed.. Pliocene floras of California and Oregon: 

Carnegie Inst. Washington Pub. 553, Contr. Paleontology, p. 21-55. 
Creely, R. S., 1955, Geology of the Oroville quadrangle, California: 

California Univ., Berkeley, Ph.D. thesis. 
Curtis, G. H., 1954, Mode of origin of the pyroclastic debris in the 

Mehrten formation of the Sierra Nevada: California Univ., Dept. 

Geol. Sci. Bull., v. 29, no. 9, p. 453-502. 
Dalrymple, G. B., 1964, Cenozoic chronology of the Sierra Nevada, 

California: California Univ., Dept. Geol. Sci. Bull., v. 47, 41 p. 
Durrell, Cordell, 1944, Andesite breccia dikes near Blairsden, Califor- 
nia: Geol. Soc. America Bull., v. 55, no. 3, p. 255-272. 
1950, Strike-slip faulting in the eastern Sierra Nevada near 

Blairsden, California [obs.]: Geol. Soc. America Bull., v. 61, no. 

12, pt. 2, p. 1522. 
1959a, Tertiary stratigraphy of the Blairsden quadrangle, Plumas 

County, California; California Univ., Dept. Geol. Sci. Bull., v. 34, 

no. 3, p. 161-192. 
1959b, The Lovejoy formation of northern California: California 

Univ., Dept. Geol. Sci. Bull., v. 34, no. 4, p. 193-220. 
1965, La Porte to the summit of the Grizzly Mountains, Plumas 

County, California: Sacramento Geol. Soc, Ann. Field Trip, 1965, 

Guidebook, 22 p. 
Gionella, V. P., 1936, Geology of the Silver City district and the 

southern portion of the Comstock Lode, Nevada: Nevada Univ. Bull., 

V. 30, no. 9, 105 p. 



Hudson, F. S., 1951, Mount Lincoln-Castle Peak area. Sierra Nevado, 

California; Geol. Soc. America Bull., v. 62, no. 8, p. 931-952. 
1955, Measurement of the deformation of the Sierra Nevado, 

California, since middle Eocene; Geol. Soc. America Bull., v. 66, no. 

7, p. 835-870. 
1960, Post-Pliocene uplift of the Sierra Nevada, California: Geol. 

Soc. America Bull., v. 71, no. 11, p. 1547-1573. 
Lindgren, Woldemor, 1897, Description of the Truckee quadrangle, 

California: U.S. Geol. Survey Geol. Atlas, Folio 39. 
1900, Description of the Colfax quadrangle, California: U.S. Geol. 

Survey Geol. Atlas, Folio 66. 
1911, The Tertiary gravels of the Sierra Nevada of California; 

U.S. Geol. Survey Prof. Paper 73, 226 p. 
MocGinitie, H. D., 1941, A middle Eocene flora from the centrol Sierra 

Nevada: Carnegie Inst. Washington Pub. 534, 178 p. 
McJonnet, G. S., 1957, Geology of the Pyramid Lake-Red Rock canyon 

area, Washoe County, Nevada: California Univ., Los Angeles, M.A. 

thesis. 
Popenoe, W. P., Imloy, R. W., and Murphy, M. A., 1960, Correlotion 

of the Cretaceous formations of the Pacific Coast (United States and 

northwestern Mexico); Geol. Soc. America Bull., v. 71, no. 10, p. 

1491-1540. 
Potbury, S. S., 1935, The La Porte flora of Plumas County, Colifornia: 

Carnegie Inst. Washington Pub. 465, p. 29-81. 
Russell, R. J., 1928, Basin Range structure and stratigraphy of the 

Warner Range, northeastern California: California Univ., Dept. Geol. 

Sci. Bull., V. 17, no. 11, p. 387-496. 
Turner, H. W., 1891, Mohawk lake beds (Plumas County, California]; 

Philos. Soc. Washington Bull., v. 11, p. 385-409. 
1394, The rocks of the Sierra Nevada: U.S. Geol. Survey, 14th 

Ann. Rept., pt. 2, p. 435-495. 
1896, Further contributions to the geology of the Sierra Nevada: 

U.S. Geol. Survey 17th Ann. Rept., pt. 1, p. 521-762. 
1897, Description of the Downieville quadrangle [California]: 

U.S. Geol. Survey Geol. Atlas, Folio 37. 
1898, Description of the Bidwell Bar quadrangle [California]; 

U.S. Geol. Survey Geol. Atlas, Folio 43. 
Weaver, C. E., and others, 1944, Correlation of the marine Cenoioic 

formations of western North America [Chart 11]; Geol. Soc. America 

Bull., V. 55, no. 5, p. 569-598. 
Whitney, J. D., 1880, The auriferous gravels of the Sierra Nevada of 

California: Harvard Coll., Museum Comp. Zoology, Mem., v. 6, no. 1, 

569 p. 




[i98] 



CENOZOIC VOLCANISM 
OF THE CENTRAL SIERRA NEVADA, CALIFORNIA 



By David B. Slemmons 

Mackay School of Mines, UNivtRsiTY of Nevada, 

Reno, Nevada 



The purpose of this article is to review the Cenozoic 
volcanic activity of the central Sierra Nevada and, 
more briefly, the volcanism in the southern part of 
the range. In a companion article in this bulletin. Dr. 
Cordell Durrell revie\\ s the Cenozoic volcanic activity 
of the northern Sierra Nevada. 

Although nearly all of the central Sierra Nevada 
has been mapped by reconnaissance methods, the exact 
age of the volcanic units has been a matter of broad 
generalization, due to sparse preservation of fossil 
faunas and floras and general lack of published de- 
tailed mapping. Because sophisticated methods for dat- 
ing volcanic rocks by potassium-argon isotope analysis 
have recently been developed, it is now possible to 
subdivide more accurately the volcanic sequences and 
to correlate between widely separated, nonfossiliferous 
units. The present paper, therefore, \vi\\ utilize the 
recent age dates of Dalrymple (1963, 1964a, 1964b), 
Evernden and James (1964), and Evernden, Savage, 
Curtis, and James (1964) as summarized in figure 1. 

The problem of describing the volcanic activity of 
this region is further confused b\' the general lack of 
formational assignment of many of the volcanic units 
and b\' the absence of data regarding detailed field 
relations of those formations now recognized. Al- 
though most of the major rock units were recognized 
by Ransome and Turner in the late 1800's, no formal 
formational names were proposed by them. The de- 
scription of map units in the foothill region was as- 
sisted by Piper and others (19.^9) who proposed the 
formational names, "\"alle\' Springs Formation" for 
the early rhyolites, and "Alehrten Formation" for 
younger andesites of the foothill area. Near the sum- 
mit areas of the range, however, the volcanic section 
is much more diverse and additional formational as- 
signments were found to be necessary during thesis 
studies by Curtis (1951), Halsey (1953), and Slem- 
mons (1953). Although the results of these studies 
are available, none of the ne\\' formational names in- 
cluded have been formally proposed. This summary 
article will utilize their data in subdividing the vol- 
canic stratigraphy into formations that are consistent 
with this more recent research. 

Some of the research \\hich contributed to this 
paper was developed during a study of the Sonora 
Pass Remote Sensing Test Site, under NASA Research 
Grant NGR-29-001-015, and also during studies of 



active tectonism in the Basin and Range province 
under NSF Grant GP-5034. 

I w ish also to express my gratitude to Gary Ballew, 
Peter Chapman, Jim Sjoberg, David Sterling, and Wil- 
liam Tafuri for assistance in compiling isopach maps 
included with this article. The editorial and technical 
assistance of Harold Bonham, Ira Lutse\', Dick Paul, 
and Ron Gunderson, of the Nevada Bureau of .Mines, 
is also gratefully acknowledged. The qualit\' of the 
detail supporting the distribution of the various vol- 
canic units was greatly improved by the preliminary 
release of data bv John Burnett, Robert .Matthews, and 
Rudolph Strand of the California Division of .Mines 
and Geolog>'. 

RESUM6 OF THE CENOZOIC HISTORY OF THE SIERRA NEVADA 

The Cenozoic volcanic history can be divided into 
four major episodes: (1) an Oligocene to .Miocene 
period of eruption and deposition of the \'alley 
Springs rhyolite tuffs, (2) a late .Miocene or early 
Pliocene period of andesite eruptions resulting in the 
accumulation of the mudflows and volcanic sediments 
of the Relief Peak Formation (new), (3) an early 
Pliocene period of eruption of latite and quartz latite 
flows and tuffs of the Stanislaus Formation (new), and 
(4) later eruptions of Pliocene andesites of the Dis- 
aster Peak Formation (new) and late Pliocene to Qua- 
ternar\' andesites, basalts, and rh>olites. 

The earliest activity in the central Sierra Nevada is 
much \ounger than that of the northern Sierra Nevada 
where andesites were erupted as earl\- as 53.5 m. y. 
ago (Dalrymple, 1964a), that is, in the late Paleocene 
or earlv Eocene. The initial activity of the central 
Sierra Nevada consisted mainh- of deposition of rhyo- 
litic tuffs, which are widely distributed in the range 
north of the Madera-iMariposa County line. These 
rhyolitic eruptions were of nuee ardente type, and 
the sporadic eruptions, which commenced about 33 
m. v. ago, spread a succession of welded tuffs that 
blanketed most of the northern and central parts of 
the range. The thickness of rhyolite that has escaped 
erosion decreases from a maximum of more than 4,000 
feet near P\ramid Lake and in the \'irginia Range of 
Nevada, to about 420 feet near \'alle\- Springs in the 
western foothills of the range. The eruptive centers 
were both along and east of the Sierran divide. .Many 
sources lay to the east, for the northeast-trending belts 



[ 199 1 



200 



lESTEDN FOOTHILLS 

Stinltlaus anil 

Holia luana df a inaga t 



Gkolocv ok Northirn Caliiornia 

mODLE tLTITUDES 

Slams laus and 

Tuolumne diainagei 



Bull. 190 



RELIEF 
FOUHTIOM 



V«ILET 
SFRtmS 
FODUTIOII 



TiDIl ■ountlir 

Lai I It Hiallir 

(200-) 



18.9. 21.9 >.l 



tnatlllic 
bttecia 
OOO' ) 



Tabia launlai 

Latila laiba 

OOO') 



9.0. 9.2 a.T. 



H ICH S lORt 

Slams laus and 
Tuo lu»ne d r a tnaga 



Harnblanda-i ich 
andat ilal 
(1000') 



Eutaki Valli) IMi 

ilOt ill-iUlili 

lajile UOO' ) 

Tabli •ounlain 

Lama laabai 

(1500') 



20.5 H.T.- 






*h«olilt tufli 



DISISTCI 

act! 

FoaiHiioii 



RELIEF 
■ PEtl 

FOaUtlON 



»»LUY 

saainos 
Foawiioii 



Figure 1. Correlation and summary diagram of Tertiary 
Valley Springs Formation type section and Knights Ferry 
Ridge; C, Composite section from Sonoro Poss ond RoncI 



cks of the central Sierra Nevada (after Dalrymple, 1964): A, Composite section from 
a; B, Composite section from Ponderosa Way, Rattlesnake Hill, McKay, and Jawbone 



of rh\()litc increase in tiiickness to the northeast, and 
some rii\oIite intrusions have been recognized near 
the summit of the range. In the central Sierra Nevada, 
the rhyolites are generally called the "Valley Springs 
Formation," but ranges in actual age dates (16.1 to 
33.4 m. >•.) indicate that activity was sporadic during 
an extended period. Slemmons (1953) and Dalrymple 
( 1 964a) have recognized more than one member both 
in the summit region and at the type locality in the 
foothills (fig. 1). This further confirms the intermit- 
tent character of the eruptions. In the foothill region 
the basal unconformit>- generall\- has low relief, w ith 
broad floored valleys and narrow inner gorges, sug- 
gesting that some uplift and rejuvenation preceded the 
eruptions. The basal unconformity commonly is above 
rocks that are w eathered to a hematite-red color and, 
iocall>-, overlies lateritic soils. This ancient weathering 
probably developed during a subtropical climatic 
phase f)f the I'.ocene. 

The rhyolitic extrusives were sufficiently extensive 
to force the establishment of new drainage systems 
that no longer followed the former trellis pattern of 
longitudinal valleys and ridges, but generally drained 
directly southwcstward across the general structural 
grain of the basement rocks. 

The andesitic deposits forming the main postrh\-o- 
lite volcanic accumulations of the range have been 
grouped together and loosely referred to as the "Mehr- 
ten Formation." The Alehrten Formation was the name 



applied by Piper and others (1939) to a sequence of 
predominantly andesitic clays, sandstones, and breccias 
exposed in a belt in the Sierra Foothills extending from 
Bellota on the Calaveras River to Cosumnes on the 
Cosumnes River. The type locality- is near the Alehrten 
damsite on the Alokelumne River. .Mthough it was 
recognized that other andesitic rocks elsewhere in the 
Sierra Nevada were correlative. Piper and others 
(1939, p. 69) clearly did not include the rocks east of 
the Foothill belt in their Alehrten P'ormation. Detailed 
mapping by Slemmons (1953) and recent age dates by 
Dalrymple (1964a), by Evernden and James (1964), 
and b\' Evernden and others ( 1964), however, indicate 
that in the Sonora Pa.ss area (fig. 1), there are three 
main postrhyoiite petrographic sequences, two of 
which are older than the Alehrten Formation at its 
type locality- 

The lowermost of the three postrhNolitc units con- 
sists of the andesites of the Relief Peak Formation that 
arc probal)l\- mainly lower Pliocene. These overlie the 
N'allcy Springs rhyolites unconformably on a surface 
exhibiting a xouthful stage of erosion. This surface 
has a relief of about 1,500 feet near the summit of the 
range, where great thicknesses of andesitic mudflows 
(lahars) predominate. In going westward from the 
cre.st, the mudflows gradually thin, and near the west- 
ern edge of the range the\' grade into andesitic sands 
and gravels. The age of the andesites is more than the 
9-m.\-.-old latites of the Sonora Pass area. 



1966 



Slkmmons: Ci'mral Sikrra Nb-.vada 



201 



Unconformably on the Relief Peak Formation arc 
tiie iatites of the Stanislaus Formation (new), which 
occur in a belt up to 20 miles in width. These Iatites 
and quartz Iatites were erupted from sources near 
Dardanelles Cone, Lighting Ridge near Sonora Pass, 
Sonora Pass, and from important but as \'ct undiscov- 
ered sources east of Sonora Pass. At least one flow 
extended westward 60 miles or more to Knights Ferry 
on the Stanislaus River, and for several tens of miles 
eastward into Nevada. Although there is some evi- 
dence that uplift of the range had already begun 
(Slemmons, 1953), and that Basin and Range faulting 
had possibly begun, the uplift could not have amounted 
to more than a third of the total Late Cenoxoic uplift 
and tilt of the range, since there is no abrupt change 
in the thickness of the Iatites as the westernmost Basin 
and Range faults are crossed. Pre-latite faulting is 
believed to be relatively minor, although near Sonora 
Pass the unconformity between the Iatites and the 
underlying andesites had up to 1,500 feet of relief. 

Andesitic and basaltic lavas were deposited on the 
Stanislaus latite, and as only a weakly defined uncon- 
formit\' separates the two units the erosional interval 
between the eruption of the Iatites and the extrusion 
of andesites and basalts was brief. Relatively few dates 
are available for the andesitic and basaltic section, but 
the Oakdale flora in the youngest andesitic sediments 
in the Sierran foothills has been dated middle Pliocene 
(Hemphillian) by Axelrod (1958)- — supported by a 
recent potassium-argon date of 5.7 m.\'. (Dalrymple. 
1964a). Dalrymple (1964a; 1964b) has also suggested 
that the most recent vigorous uplift and tilting of the 
Sierra Nevada was initiated during the middle to late 
Pliocene (between 3.5 and 9 m.y. ago). Typical Basin 
and Range faulting may be somewhat younger; it 
probably began in the Mono Lake area, less than 2.6 
and 3.2 m.y. ago, and in the Truckee area near the 
end of the interval between 7.4 m.y. and 2.2 to 2.3 
m.y. ago. Thus there seems to be a time lag between 
the tilting of the Sierra Nevada and the beginning of 
the present Basin and Range faulting. 

Following the deposition of these young andesites in 
the Sierra Nevada, uplift and tilting of the Sierran 
block has caused erosion to cut deeply into the range. 
Downcutting by extensive glaciers and streams has in- 
cised the canyons far below the gently inclined surface 
at the top of the volcanic section, and the erosion cycle 
is still in a youthful stage with a consequent stream 
pattern. 

EARLY RHYOimC ACTIVITY 

Extensive remnants of rhyolite welded tuff, water- 
sorted tuffs, and rh\olite-bearing gravels commonly 
form the basal unit of the Cenozoic section in the 
central Sierra Nevada (fig. 1). The deposits generally 
grade from tuffs near the eastern part of the range 
into types that show more extensive sedimentar\- re- 
working toward the western edge of the range. The 
basal rhyolites ^\'ere named "Valley Springs Forma- 
tion" by Piper and others (1939, p. 72-73), for the 



foothill town of Valley Springs where two welded 
tuffs were described. The section there includes the 
two rhyolitic tuffs, and also cla\s, sandstones, and con- 
glomerates, lying unconformably on the lone Forma- 
tion (Eocene), on auriferous gravels, or locall\- on 
pre-Tertiary basement rocks. 

The V^alley Springs rhyolites are widely distributed 
from the northern end of the range to about 37° lat. 
near the western foot of the range. On the western 
slope the rhyolite occupies narrow belts, 10 miles or 
so in width, extending from the summit w estward to 
the foothills, where the rhvolite disappears underneath 
the younger sedimentary and volcanic rocks that form 
the uppermost parr of the filling in the Great \'allcy. 
Few outcrops of rhyolite are present in the main 
Sierran slopes south of the 38° lat., near the north end 
of Yosemite National Park, although a narrow belt of 
rhyolites extends along the edge of the Great \'alley 
at least as far southward as Friant (.Macdonald, 1941). 

The thickness of the rhyolites is highly variable, 
owing not only to vagaries of initial distribution from 
various vents east of the Sierra Nevada causing the 
pyroclastic materials to be channeled down different 
westward-trending valleys, but also to extensive ero- 
sion that occurred during different intervals after 
their deposition. The thicknesses generally- decrease 
southwestward from maximum values of 1,200 feet 
near Sonora Pass and more than 1,000 feet near River- 
ton, to 450 feet at the type locality near V^alley 
Springs and 270 feet at La Grange near the Merced 
River. The rhyolite of the Hartford Hill Formation 
in the \'irginia Range is of comparable geologic age 
(Schilling, 1965), and similar rhyolite that is widely 
distributed in western Nevada has thicknesses of over 
3,000 feet (figs. 1 and 2). 

The rhyolites unconformably overlie either older 
Tertiary gravels and sands or the lone Formation. The 
rhyolites were sufficiently thick to block the valleys 
in w hich they flowed, requiring the establishment of 
new drainage patterns during the subsequent erosion 
c\cle. The surface developed on the rh\olite was one 
of moderate relief, with up to 1,000 feet of local relief 
toward the source areas. The extensive erosion which 
followed both the rh\olitic and andesitic eruptions 
stripped much of the rh\olite from valley walls, but 
small bands of protected portions of rh\olites still 
remained sporadically below the very irregular base of 
overlying andesites or Iatites. 

The \^alle\' Springs Formation was assigned a late 
Miocene age on the basis of a small flora (Axelrod, 
1944, p. 217). Recently, more than 25 potassium-argon 
dates have become available for early Sierran rhyolites, 
(Evernden and others, 1962; Evernden and James, 
1964; and Dalrymple, 1964a). These dates show a 
broad range in time, from as much as 33.4 m.y. (late 
Oligocene) to as little as 16.1 m.y. (middle Miocene). 
According to Dalrymple (1964a, p. 21), part of this 
disparit)' of ages is due to discordance in dates from 
various minerals in the same rock, probably as a result 



202 



Gkologv ok Northern Calikorma 



Bull. 190 




Figure 2. Mop jhowing diifribution of Oligocene to Miocene rhyoliles of the central Sierra Nevodo, with solid contouri denoting their 
opproximote moximum original thickness. The dashed contours indicole the opproximate elevation of the inferred top of the rhyolites. The deep 
and repeated dissection of the rhyolites mokes the Indicoted isopochs minimol volues for the thickness in deeper valleys. Although there may hove 
been several oreas of nondeposition between some of the southwest-trending channels of maximal thickness, the isopochs and contours of ele- 
vation ore projected between the main channels. 



1966 



Slkm.mons: Ckntrai. Surra Nivada 



203 



of contamination by older bedrock minerals. Most of 
the variation, however, is believed to indicate a pro- 
longed, but intermittent, period of rh\olitic activity, 
with the main eruptions occurring in the early Mio- 
cene. 

fMost, if not all, the rh\olites had a northeastcrl\- 
source. This is indicated by the progressive increase 
in thickness of the rhyolites in a northeast, upslope 
direction, the presence of some Tertiary rhyolite in- 
trusions toward the eastern edge of the range, and the 
progressive change from rhyolitic sediments in the 
southwest, to massive tuffs and welded tuffs toward 
the northeast. \^ 

EARLIER ANDESITIC ACTIVITY 

Postrhyolite flows, mudflows, gravels, and sands, 
derived mainly from centers of basic andesite erup- 
tions in the central Sierra Nevada, extend in a continu- 
ous zone from at least as far east as Ebbetts Pass and 
Sonora Pass to the western foothills at Knights Ferrw 
This sequence of andesites and associated rocks is 
herein named the Relief Peak Formation. It uncon- 
formably overlies the \"alley Springs Formation, and 
is unconformably overlain by the Stanislaus Formation. 
The thickness of the Relief Peak Formation decreases 
from the crest of the range toward the \\ estern foot- 
hills, where it contains a Mio-Pliocene flora and under- 
lies latites with ages of about 9 m.y. 

The Relief Peak Formation crops out on the slopes 
of Relief Peak, designated herein as the type area, in 
a sequence that is not only of the unusually great 
thickness of about 3,000 feet, but also is of varied 
lithology. The sequence includes on the north flank 
of the mountain, in sees. 18, 19, and 20, T. 5 N., R. 21 
E., about 20 feet of gravel with abundant granitic and 
metamorphic rocks of the Emigrant Basin type, andes- 
itic sands, and, near the base, much reworked rhyolitic 
material, including cobbles and sands from the under- 
lying Valley Springs Formation. Above these volcanic 
sediments, the section is composed mainly of mudflow 
breccias and autobrecciated andesitic flows. 

The thickness of the Relief Peak Formation varies 
from 3,000 feet near the source at Relief Peak, and at 
Mount Emma near Sonora Pass, to about 300 feet near 
the Jamestown-Knights Ferry area shown on figure 
la, where the formation disappears under younger 
deposits of the Great Valley of California. 

This unconformity, between the early andesites of 
the Relief Peak Formation and underlying basement 
rocks or Cenozoic rhyolites and sediments, is generally 
one of moderate relief in the foothills, but to the ea.st 
the relief increases to about 2,000 feet and provides a 
buried youthful erosion surface with slopes of over 
25°, which is as steep as the present mountain slopes. 
The unconformity preserves dendritic channels in the 
underlying rhyolites that followed paths which led 
more or less directly downslope to the southwest. The 
erosional interlude between the deposition of the 20- 
to 33-m.y. old rhyolites and the Relief Peak andesites 
was sufficiently long to create new, youthful valleys 



with a relief as great as that on the prerhyolite ter- 
rain. In the old vailevs at the base of the andesites in 
places are included sands and gravels, generall\' con- 
taminated both with basement rocks and easil\' eroded 
Cenozoic rhyolites. 

From andesites underlying the Table Mountain La- 
tite Member of the Stanislaus Formation near James- 
town that are herein assigned to the Relief Peak For- 
mation, Condit (1944) has described a Mio-Pliocene 
flora, the Table Mountain flora. Stirton and Goeriz 
(1942) assign an early Clarendonian age to the same 
rocks on the basis of a small fauna. The potassium- 
argon dates for the overlying Stanislaus Formation 
ranges between 8.8 and 9.3 m.v., and the underlying 
rhyolites are probably older tlian 19.9 m.y., which is 
the age of the youngest of the underlying V'alley 
Springs rhyolites. 

On the basis of a flora found on Niagara Creek, the 
basal sediments of the andesites of the Relief Peak 
Formation higher in the range appear to have a late 
Miocene age (D. I. Axelrod, oral communication, 
1965). In this area the underlying rhyolite yields a 
potassium-argon date of 23.3 m.y. on sanidine and 
25.7 and 26.1 m.y. on biotite samples; of the three 
dates, Dalrymple (1964a, p. 22) considers the sanidine 
date as the most reliable. In either case, the lower 
Miocene age of the rhyolite is well established. The 
Stanislaus Formation, which unconformably overlies 
the Relief Peak, is Hemphjllian, with potassium-argon 
ages of about 9 m.\-. The weaki\- eroded nature of 
the unconformity at the base of the latites in this area 
suggests that the youngest of the Relief Peak ande- 
sites may be lower Pliocene, and these early andesites 
may have been erupted at various stages during late 
Miocene to lower Pliocene. 

Dikes and plugs of andesite are abundant in the area 
from Sonora Pass and Relief Peak to Mount Emma, 
and this must have been at least one of the major 
source areas for the Relief Peak mudflow breccias, 
tuffs, and flows. Extensive andesitic volcanic activit\- 
in nearby parts of Nevada could have provided addi- 
tional sources for some of the mudflows, sands, and 
gravels of the Relief Peak Formation. 

STANISLAUS FORMATION 

Latites erupted after the Relief Peak andesitic ac- 
tivity, and herein named the Stanislaus Formation, 
may prove to be of singular importance in decipher- 
ing the structural and geomorphologica! development 
of the central Sierra Nevada, for they seem to form 
the onl>- well-defined stratigraphic and time marker 
that extends from under the Great X'alley of Cali- 
fornia, across the range, and into the eastern portion 
of the Basin and Range province. Because the Stanis- 
laus Formation predates b\- a short interval most of 
the Sierra Nevada uplift and the development of the 
present Basin and Range topography by faulting, it 
not only provides a measure of fault displacements but 
also a means of correlating between the r\\o provinces. 



204 



Gkol<x;y of NoRiiiiKN Caiiiorma 



Bull. 190 



^i^f^ 




Figure 3. Map showing inferred 
distribution of the Table Mountain Lo 
Valley Member, The volcanic centers 
diagonal pattern near Sonoro Pass, 
similarly indicated about 15 miles eo 



al distribution of the Stanislaus Formation, and the original 
ember and the welded biotite-quartz lotite tuffs of the Eureka 
le Table Mountain Member are in the area indicoted by the 
3 possible intrusive source for the Eureka Valley Member is 



Pass. 



The latites now assigned to the Stanislaus Formation 
\\ere divided into three units by Ransonie (1898) and 
Slemmons (1953). The three units, now considered 
to he members, are herein defined from oldest to 
\()ungest as: ( 1 ) Table A4ountain Latite Member, 
mostl\' olivine-augite latite flows including the type 
locality for latites, (2) Eureka \'alley Member, con- 
sisting of several latite flows with interbedded welded 
biotite-augite quartz-latite tuff, probably the type 
"quartz latites," and (3) Dardanelles Member, con- 
taining flows ranging from latitic to basaltic in com- 
position. 

The Stanislaus Formation is named for its conspicu- 
ous development along the various tributaries of the 
Stanislaus River of California, and the type locality 
is designated as the Bald Peak-Red Peak ridge which 
separates the Clarks Fork and Deadman Creek branches 
of the Middle Fork of the Stanislaus River. The three 
formally named members arc defined on the basis of 
the three most characteristic localities for each of the 
nicmbcrs, and w ith an attempt to fit the terminolog\- 
as closcl\- as possible to the nomenclature proposed 
informally in the classic description of type latites and, 
pr()babl\-, quartz latites, by Ransome (1898). 

The lowermost unit is here designated the Table 
■Mountain Latite .Member, in conformity with Ran- 
some's (1898, p. 14-27) references to the "Table 
Mountain facics" of the latites, and to the "Table 
Mountain flow." This member is, accordingly, named 
for "Tuolumne Tabic .Mountain," half a mile west of 
Shaws Flat in the Columbia (1:24,000) quadrangle, 
California, where it is almost 200 feet thick. The Table 



Mountain Latite Member has been traced from its type 
localit\- at Table Mountain almost continuously (Ran- 
some, 1898; Slemmons, 19.v3) to its source area near 
Sonora Pass, where at Sonora Peak and Leavitt Peak 
there are as man\' as 40 flows of this same t\pe of 
latite lava comprising a thickness of 1,.500 feet. 

The middle member, the "biotite-augite-latite" of 
Raasome (1898, p. 37-46), is here named the Eureka 
X'alley Member for Eureka \'alley in the Dardanelles 
quadrangle (1:62,500). The type locality is the ridge 
between Bald Peak and Red Mountain where the sec- 
tion shows great diversity of lithology and a thickness 
of 200 feet (Slemmons, 1953, p. 67-71). This mem- 
ber conformably overlies the Table Mountain Latite 
Member. 

The uppermost member of the Stanislaus Formation 
is here named the Dardanelles .Member (as currently 
spelled) after the "DardancUc flow" of Ransome 
( 1898, p. 46-52) for the West Dardanelle of the Dar- 
danelles Cone quadrangle. At the West Dardanelle, 
u hich is designated as the type locality, the flows are 
similar to the augite latites of the Table Mountain 
■Member, but plagioclase phenocrysts in them are 
smaller and more sparse. Eastward from West Dar- 
danelle, the Dardanelles Member includes a number 
of basalt and olivine basalt flows. This member con- 
formably overlies the Eureka X'alley Member. 

The Stanislaus Formation attains a maximum thick- 
ness of more than 1,500 feet near Sonora Pass, but it 
thins southwestward to where, in the Table Mountain 
area near Sonora, it consists of a single augite latite 
flow only 200 feet thick. It is unfossiliferous, but Dal- 



1966 



Sl.F.M.MONS: Cf.NTRAI, SlKRRA NfVADA 



205 



ryniple has dated six samples b\- the potassium-argon 
method and obtained dates of from 8.8 to 9.3 m.y., 
indicating a lower Pliocene (Hemphillian) age. Some 
of the latite lava erupted from dikes and fissures be- 
tween Dardanelles Cone and Sonora Pass, and other 
flows mav have erupted east of the present divide 
(Halsey, 1953). 

The great area! extent of the Stanislaus Formation is 
shown by figure 3. The lower unit, the Table Moun- 
tain Latite .Member, extends eastward from near 
Knights Ferry, where it emerges from beneath 
\ounger volcanics and sediments that mantle the Great 
\'alle>'. It attains a maximum width near Sonora Pass 
in the source area and fans out east of the summit 
area. Still farther east it narrows and becomes sporadi- 
cally distributed as it approaches its eastern limit near 
the Nevada-California boundary. The overlying 
welded augite-biotite quartz latite tuffs do not ex- 
tend as far w estward as the flows of Table /Mountain 
augite latite, but their total area is greater. The quartz 
latite outcrop width increases greatly as the summit 
of the range is approached, its limits extending farther 
north, east, and south than the flows of the Table 
Mountain Latite .Member. The basalts and latites of 
the uppermost unit, the Dardanelles .Member, are be- 
lieved to be more limited in areal extent, having a 
known distribution from Big Trees on the west to the 
Nevada-California boundary on the east (Ransome, 
1898; Slemmons, 1953; and Halsey, 1953). Future de- 
tailed mapping, however, will probably extend the 
limits as indicated in figure 3. 

The thickness of the Stanislaus Formation varies 
greatly because of the irregular unconformit)' at the 
base of the formation, the irregular initial deposition, 
and because of subsequent deep dissection. The Table 
Mountain Latite .Member at Knights Ferry has a 
thickness of 200 feet, and near the source at Sonora 
Pass has its maximum thickness of 1,500 feet. It thins 
out to the east at Fales Hot Springs, but a small aux- 
iliary field of similar augite latites is developed near 
Bridgeport, California. The Eureka Valley Member 
varies in thickness from a few tens of feet near Big 
Trees to 400 feet in the Sonora Pass area and Bell 
Meadows, 3 miles southeast of Pinecrest Reservoir. 
The overlying latites and basalts of the Dardanelles 
Member are developed mainl\' between the Darda- 
nelles, where they are 200 feet thick, and the eastern 
edge of the Fales Hot Springs quadrangle. 

The unconformit>' which separates the latites of the 
Stanislaus Formation from the underlying Relief Peak 
andesites is generally one of low relief, and may indi- 
cate only a short hiatus in deposition. No lateral 
equivalents to the latites are known. 

The age of the Stanislaus Formation can be placed 
rather closely in spite of the absence of fossil localities 
in it because the consistenc\' of the several available 
potassium-argon dates restricts the latitic activities to 
a brief period. The date for the Table Mountain Alem- 
ber is 9 m.y., the four values for the biotite-augite 



quartz latite welded tuffs of the Eureka Valley Mem- 
ber are 9.2 m.y. at Big Trees, 8.8 and 8.9 m.y. for 
tiie summit region, and 9.0 m.y. for the Jawbone 
Ridge area. The Dardanelles Member, the uppermost 
unit, is represented by a 9.3 m.y. date (Dalrympie, 
1964a). The onlv other potassium-argon age date sim- 
ilar to those of the latites is from the Table Mountain 
basalt (Sugar Loaf Hill) of the Friant area (Dal- 
rympie, 1963; Wahrhaftig, 1965) and Coyote Flat. 
This unit is probabl\' an olivine basalt (Macdonald, 
1941; Dalrympie, 1963; and Wahrhaftig, 1965), al- 
though Dalr\-mple's whole-rock anal>"ses indicate a 
potassium content of 2.01 percent at Sugar Loaf Hill 
and 1.82 percent at Co\ote Flat, suggestive of alkaline- 
potassium affinities. Their potassium-argon ages are 
9.5 m.y. and 9.6 m.\-., respectively. 

The source of at least part of the Stanislaus Forma- 
tion is indicated by the occurrence of more than 20 
augite latite dikes recognized between Dardanelles 
Cone and Sonora Pass. Halse\- (1953) also has noted 
the possibility of quartz latitic centers of eruption near 
Fales Hot Springs. The thickest sections are between 
Sonora Pass and Pinecrest, which suggests that there 
mav be other sources to the west of the present 
divide. 

POSTLATITE VOLCANIC ROCKS 

Postlatite lavas, mostly andesites and basalts, form a 
thick succession near Sonora Pass, and extend across 
the entire width of the range to the Great X'alley of 
California, where they form the type locality for the 
.Mehrten Formation (Piper and others, 1938). These 
lavas probably extend northward to, or be\ond, Don- 
ner Pass, but the lack of adequate potassium-argon 
dates or paleontological control, and the absence of 
latitic lavas, have made it difficult to distinguish them 
from the older andesites of the central Sierra Nevada. 
In addition to this thick sequence of lavas, there are in 
the Sierra a number of isolated outcrops of flows of 
basalt, andesite, and rh\olite that are mainl>- \ounger 
than this thick sequence. .\s many of these postlatite 
rocks occupy especially significant positions on ero- 
sion surfaces of var_\ing geomorphological age, they 
have received special attention (Axelrod and Ting, 
1960, 1961; Dalrympie, 1963a, 1963b, 1964; Wahr- 
haftig, 1965). 

The thickest and most w idespread of the post-Stan- 
islaus Formation lavas of the Sonora Pass area are 
hornblende-rich andesites herein designated as the Dis- 
aster Peak Formation (fig. Ic). They arc ver\- well 
exposed in a section preserved on the slopes of Disaster 
Peak, Sonora Pass quadrangle, which is designated as 
the type locality. This formation can be recognized 
in the source area between Ebbetts Pass and Relief 
Peak by the presence in it of large cobbles and breccia 
clasts of hornblende andesites, generalK" with abundant 
hornblende phenocrysts up to 1 inch in length. The 
hornblendes are sufficiently large to "twinkle" in the 
sunlight as the outcrops are crossed, even when one is 



206 



Gkology of Northfrn CaI.IF()RM\ 



Bull. 190 








Miiaua thicknats aboya oaap val 


1 ayt 


3000 




Ptaiani alaval Ion of intarrad 
t op of t hata vol can 1 c r ocka 







J^rL^\i,^°'' '''°*'^^ dislribuflon of late Cenozoic ande.ite, latit., bo.olt, ond Pliocan. rhyollle. The opproximcte moximum originol thicknes. 
r„U red too or7h.r"°"l " r ' '"^°'"^ ''V"'' "'''' "°''°''"- ''"• ''"'••'' contour, denote the opproxin,o»e preTen^ e ^^on of the 

:t:ti:T„:Uh"i:t,et7;v;rct';ci:ck°tr;ep:.:r: -''-'■• '''""' -"-"^ °' '"^ '°° ^'" «-• "-'-■'"' -•'- <■-« - ^^«^'' 



1966 



Slkm.mons: Cf.ntrai, Sikrra Nfvada 



207 



crossing rapidly in a car. The deposits arc mainl\- 
mudflow breccias, autobrecciated flows, and subordi- 
nate volcanic sediments. The section is approximately 
1,000 feet thick, both near Disaster Peak and also 
farther south near Castle Rock and East Flange Rock 
where the Disaster Peak andesites lie on latite. The 
Disaster Peak Formation may prove to be the equiva- 
lent of the Mehrten Formation in the type area, but 
owing to large gaps in the mapping it seems best to 
apply a new name rather than guess at the correlation. 

The composition of the younger volcanic rocks 
varies from dominantly hornblendic andesites, which 
contrast with the p>'roxene-bearing t>pes that predom- 
inate in the older andesitic volcanics of the central 
Sierra Nevada (Curtis, 1951), to rhyolite and basalt. 
South of the Sonora Pass area, the volcanic rocks are 
limited in extent and are mainly basalts, rhyolite in 
domes, and pyroclastic beds. The deposits attain maxi- 
mum thicknesses in excess of 1,500 feet between the 
Sonora Pass area (fig. Ic) and the south end of Lake 
Tahoe. East of the Sierra Nevada, volcanics of similar 
age are even thicker, suggesting that many of the vol- 
canics present in the Sierra Nevada may have had an 
eastern source. That the latest volcanic activity is more 
diversified than in earlier parts of the Cenozoic is 
shown in figure 1. 

The thickness of the young volcanic rocks is highl\- 
variable, for much of the southern part of the range 
is either unafi^ected by volcanic activity, or contains 
only sporadic flows, mainly of basalt. There is a gen- 
eral increase in thickness of the Disaster Peak Forma- 
tion to the east in the central part of the range, with 
a variation of from several hundred feet near the t\pe 
locality of the Mehrten Formation at the edge of the 
Great Valley to over 3,000 feet near Sonora Pass and 
Lake Tahoe. 

The Disaster Peak Formation unconformably over- 
lies either the Stanislaus Formation, usualh' with an 
erosion surface of low relief, or the early andesites and 
Valley Springs rhyolites with a deeply dissected sur- 
face of moderate relief. 

The postlatite lavas vary widely in age, and include 
andesites only slightly younger than the 9-m.y.-old 
latites of the Stanislaus Formation, as well as andesitic 
material from the Verdi area in adjoining Nevada that 
has been dated at 5.7 m.y. (Evernden and James, 1964), 
and the Oakdale flora and faunas of the foothill region 
(Axelrod, 1944; Stirton and Goeriz, 1942). The 
younger basalts include a wide range of dates from 
scattered sources in the summit region. 

The source of these young volcanic rocks of the 
Sierra Nevada lies mainly in many separate vents, most 
of which are near the crest of the range or east of 
the range. 

PETROCHEMISTRY 

The petrochemical character of the Sierra Nevada 
volcanic activity is different for each of the separate 
and independent periods of eruption. Activity during 
Mesozoic appears to be distinct in character from that 




Figure 5. Silica variation diagram for Cenozoic volcanic rocks of 
the alkolic Stanislaus Formation (solid lines), the calc-olkoline volconic 
rocks of the Mehrten Formation (dashed lines), and calc-alkaline 
Mesozoic plutonic rocks of the central Sierra Nevada (dotted lines). 
The principal sources of analytical data ore from Curtis (1951), 
Halsey (1953), Slemmons (1953), and Washington (1917). 

of the three main periods of the Cenozoic (fig. 1), 
although the small number of analyses of Mesozoic 
intrusive rocks prevents a good comparison. 

The Oligocene and Miocene magmas of the Valley 
Spring Formation were dominantl\- rhyolitic. The 
overlying Relief Peak andesites, though not repre- 
sented by many chemical analyses, were mainly ba- 
saltic, and basic to intermediate, andesites. The latites 
of the Stanislaus Formation are much different from 
both younger and older volcanic rocks because they 
are alkalic, and potassium predominates over sodium 
in most of them (fig. 5). Their alkaline character is 
indicated by the Peacock calc-alkali index being lower 
for these rocks than for most Sierra Nevada volcanic 
rocks. Postlatitic activity has, except for the major 
period of eruption of the Disaster Peak hornblendic 
andesites, been marked by diverse activity in which 
extreme chemical types seem to be dominant. Rhyo- 
lites and basalts were erupted intemiittenth" during the 
last part of the Pliocene and the Quaternary. This 
activitv is well marked east of the range both at .Mono 
Lake and in Owens \'alle\-, as well as within the main 
Sierran block. 

frhe eruptive record provides sharp contrasts in 
chemical character, from the mainly rhyolitic charac- 
ter of the early activity- in the Oligocene and Miocene, 
to the andesitic character of the Mio-Pliocene or early 
Pliocene, to latites and quartz latites with highly alka- 
line and strongly potassic aflJinities, to the youngest 
periods of andesitic, rhyolitic, and basaltic activity 
with a calc-alkaline characten 



208 



Gi'oi,(h;y ok Noriukrn Cai,ikirni\ 



Bull. 190 



REFERENCES 



Axelrod, D. I., 1944, The Oakdole flora | California 1: Cornegle Inst. 
Washington Pub. 553, Contr. Paleontology, p. 147-165. 

1957, Late Tertiory floras and the Sierra Nevada uplift |California- 

Nevodol: Geo!. Soc. America Bull., v. 68, no. 1, p. 19-45. 

1958, The Pliocene Verdi flora of western Nevodo: Colifornio 

Univ. Pub. Geo!. Sci., v. 34, no. 2, p. 91-159. 

1962, Post-Pliocene uplift of the Sierra Nevada, California; Geol. 

o. 2, p. 183-198. 

S., 1960, Late Pliocene floros east of 
ia: Colifornio Univ. Pub. Geol. Sci., v. 



73, 



from the Chogoopa 
v. Pub. Geol. Sci., V 

v., 1962, Geologic i 
o sheet: California 

,., 196 , Geologic 
sheet: Colifornic 
;ss 1965) 



irfoce, souther: 
39, no. 2, F 



ap of Colifo 
Div. Mines 



lap of California, 
Div. Mines and 



Geol. So 



Cenozoic 
. America 



Soc. Americo E 
Axelrod, D. I., and Ting, W 

the Sierra Nevada, California 

39, no. 1, p. 1-118. 
1961, Eorly Pleistocene flora: 

Sierra Nevada: California Uni 

119-194. 
Burnett, J. L., and Jennings, C. \ 

Olof P. Jenkins edition, Chi< 

Geology, scale 1:250,000. 
Burnett, J. L., and Matthews, R. / 

Olof P. Jenkins edition, Fresno 

Geology, scale 1:250,000. (In pr. 
Condif, Corlton, 1944, The Table Mountain flora |Californial : Carnegie 

Inst. Washington Pub. 553, Contr. Paleontology, p. 57-90. 
Curtis, G. H., 1951, Geology of the Topaz Lake quodrongle and the 

eastern half of the Ebbetts Pass quadrangle: Colifornio Univ., Berke- 
ley, Ph.D. thesis, 310 p. 
Dolrymple, G. B., 1963, Potassium-argon dotes of 

volconic rocks of the Sierro Nevada, Colifor 

Bull., V. 74, no. 4, p. 379-390. 
1964o, Cenozoic chronology of the Sierra Nevodo 

California Univ. Pub. Geol. Sci., v. 47, 41 p. 
1964b, Potossium-orgon dates of three Pleistocene 

basalt flows from the Sierra Nevada, California: Geol. So 

Bull., V. 75, no. 8, p. 753-758. 
Evernden, J. F., and James, G. T., 1964, Potassiun 

the Tertiary floras of North America: Am. Jour. J 

p. 945-974. 
Evernden, J. F., Savage, D. E., Curtis, G. H., and James, G. T., 1964, 

Potossium-orgon dotes and the Cenozoic mommolion chronology of 

North America: Am. Jour. Sci., v. 262, no. 2, p. 145-198. 
Holsey, J. G., 1953, Geology of ports of the Bridgeport, California, 

ond Wellington, Nevada quadrangles: Colifornio Univ., Berkeley, 

Ph.D. thesis. 
Koenig, J. B., 1963, Geologic mop of California, Olof P. Jenkins 

edition. Walker Lake sheet: California Div. Mines and Geology, scole 

1:250,000. 
Lindgren, Woldemar, 1894, Description of the Sacromento quadrangle, 

California: U.S. Geol. Survey Geol. Atlas, Folio 5, [3] p. 
1897, Description of the Truckee quodrongle, Colifornio: U.S. 

Geol. Survey Geol. Atlas, Folio 39, 18] p. 



Colifornio: 



interglociol 



1 dot. 
262, 



1900, Description of the Colfox quadrangle, California: U.S. Geol. 

Survey Geol. Atlos, Folio 66, 10 p. 

lindgren, Woldemor, and Turner, H. W., 1894, Description of the 
Placerville quodrongle, California: U.S. Geol. Survey Geol. Atlas, 
Folio 3, 9 p. 

1895, Description of the Smartsville quadrangle, Colifornio: U.S. 

Geol. Survey Geol. Atlas, Folio 18, |6] p. 

Lindgren, Woldemar, and Hoover, H. C, 1896, Description of the 
Pyramid Peak quadrangle, Colifornio: U.S. Geol. Survey Geol. 
Atlos, Folio 31. 

Mocdonold, G. A., 1941, Geology of the western Sierra Nevada be- 
tween the Kings ond Son Joaquin Rivers, Colifornio: California 
Univ., Dept. Geol. Sci. Bull., v. 26, no. 2, p. 215-286. 

Piper, ". M., Gale, H. S., Thomas, H. E., and Robinson, T. W., 1939, 
Geology and ground-water hydrology of the Mokelumne oreo, Coli- 
fornio: U.S. Geol. Survey Woter-Supply Paper 780, 230 p. 

Ronsome, F. L., 1898, Some lovo flows of the western slope of the 
Sierra Nevodo, Colifornio: U.S. Geol. Survey Bull. 89, 74 p. 

Rogers, T. H., 196 , Geologic mop of Colifornia, Olof P. Jenkins 
edition. Son Jose sheet: California Div. Mines and Geology, scale 
1:250,000. (In press 1965) 

Schilling, J. H, 1965, Isotopic age determinotions of Nevodo rocks: 
Nevada Bur. Mines Rept. 10. 

Slemmons, D. B., 1953, Geology of the Sonoro Poss region: California 
Univ., Berkeley, Ph.D. thesis, 201 p. 

Stirton, R. A., ond Goeriz, H. F., 1942, Fossil vertebrates from Super- 
jacent deposits near Knights Ferry, Colifornio: California Univ., 
Dept. Geol. Sci. Bull., v. 26, no. 5, p. 447-472. 

Strand, R. G., 196 , Geologic mop of California, Olof P. Jenkins 
edition, Mariposa sheet: Colifornio Div. Mines and Geology, scale 
1:250,000. (In press 1965) 

Turner, H. W., 1894, Description of the Jackson quodrongle, California: 
U.S. Geol. Survey Geol. Atlas, Folio 11, |61 p. 

Turner, H. W., and Ronsome, F. L., 1897, Description of the Sonora 
quodrongle, Colifornia: U.S. Geol. Survey Geol. Atlas, Folio 41, 
17] p. 

1898, Description of the Big Trees quadrangle, Colifornia; U.S. 

Geol. Survey Geol. Atlas, Folio 51. 

Wohrhoftig, Clyde, 1963, Origin of stepped topogrophy of the west- 
central Sierra Nevodo, Colifornio [abs.|: Geol. Soc. America Spec. 
Paper 73, p. 71. 

1965, Stepped topogrophy of the Sierra Nevada (Stop 11-4 to 

Stop 11-6), I'n Guidebook for Field Conference I, Northern Great 
Bosin and California: INQUA (Internot. Assoc. Quarternory Reseorch), 
7th Cong. 1965, p. 123-128. 

Woshington, H. S., 1917, Chemical analyses of igneous rocks: U.S. 
Geol. Survey Prof. Paper 99, 1201 p. 



ECONOMIC MINERAL DEPOSITS OF THE SIERRA NEVADA 



By William B. Clark 
California Division of Mines and Geo 



The Sierra Nevada province has been a major source 
of minerals since Marshall's historic gold discovery at 
Sutter's mill in 1848. At the present time this region 
is the source of large quantities of sand and gra\el, 
crushed and broken stone, tungsten, limestonf- and 
limestone products which include cement, lime, and 
rock used in sugar refining. In addition, substantial 
amounts of asbestos, barite, dimension stone, mineral 
filler, rhyolitic ash, soapstone, and uranium are being 
produced; and smaller amounts of gold, silver, copper, 
zinc, molybdenum, silica, gem and ornamental min- 
erals, and wollastonite are also recovered. Unfortu- 
natel\', complete production statistics for man>' of 
these mineral commodities are not available. 

The output of gold, which was once the principal 
commodity, has a cumulative value of more than $2 
billion. However, gold mining has decreased greatly 
in recent years. Other comnx)dities formerly produced 
in large amounts are copper, zinc, magnesite, chromite, 
dimension granite and marble, slate squares, and sulfur. 
Also found in the Sierra Nevada, though little ex- 
ploited, are deposits containing arsenic, antimon>-, 
andalusite, clay, garnet, cobalt, lead, nickel, platinum, 
feldspar, pyrite, manganese, mercury, quartz crystal, 
tellurium, thorium, and zirconium. .Much of the min- 
eral wealth exploited in the past or available for the 
future is in the western foothills, especially in the cen- 
tral and northern portions of the range (see fig. 2). 
Fewer deposits are found in the southern end of the 
range and along the eastern flank, although even here 
there are scattered deposits of major importance; for 
e.xample that of the Pine Creek tungsten mine. 

In the western foothills there are primary gold, cop- 
per, and zinc deposits believed to be genetically related 
to the intrusions of the Sierran granitic batholith but 
occurring largely in the belt of metamorphic rocks. 
Slate, greenstone, and amphibolite are the principal 
host rocks. In some districts, such as Grass Valley, 
Ophir, West Point, and Soulsbyville, the gold-quartz 
veins are in or around small granitic intrusions that are 
branches of the main batholith. In other districts, such 
as those at Alleghany, Washington, and Forest Hill, 
the gold-quartz veins are adjacent to serpentine bodies. 
Although this entire foothill region is often referred 
to as the Alother Lode, technically the Lode is a sys- 
tem of linked or en echelon gold-quartz veins and in- 
tervening mineralized schist and greenstone that ex- 
tends from Georgetown and Greenwood southeast to 
Mariposa, a distance of 1 20 miles. The most productive 



portions of this belt have been the Jackson, Carson 
Hill, Angels Camp, and Jamestown districts. 

The placer deposits of the Sierra Nevada have 
yielded vast amounts of gold; some estimates have 
'iced its total value at nearly $1 billion. There are 
i«o main t>'pes of placer deposits, the older or Ter- 
tiar\- deposits which are on the interstream ridges, and 
the younger or Recent ones in and adjacent to the 
present stream channels. The Tertiary deposits consist 
predominantly of quartzitic gravels deposited in the 
channels that existed man\- million \ears ago and were 
capped by thick beds of andesite. They have been 
worked mainly by hydraulic and drift mining. The 
Recent gravels have been worked by dredging, river 
mining, and small-scale methods, and were the source 
of the tremendous yields of gold in the days of "49." 
The gravel tailings from these old placer mines are 
now important sources of aggregate. 

A discontinuous belt of copper and zinc mineraliza- 
tion extends along the lower western foothills. Here 
lenticular sulfide bodies that occur in zones of alter- 
ation in greenstones, amphibolites, and chlorite schists 
have \-ielded more than 200 million pounds of copper 
and 50 million pounds of zinc. The most productive 
mines have been at Campo Seco and Copperopolis in 
western Calaveras County. Remote from the foothill 
belt, in northeastern Plumas County are the famous 
Walker, Engels, and Superior copper mines which 
have yielded more than .^00 million pounds of copper. 
At the Walker mine the ore bodies are chalcopyrite- 
bearing quartz veins in schist and hornfels near granitic 
rocks, while those at the Engels and Superior mines are 
bands of chalcopyrite and bornite in granitic rocks. 
Some by-product copper is recovered from the Pine 
Creek tungsten mine near Bishop. 

The serpentine belts of the western Sierra Nevada 
contain or are associated with a variety of mineral 
deposits. These include chromite, asbestos, nickel, gem 
minerals, ornamental stones, magnesite, and soapstone. 
The Pillikin mine in El Dorado County has been the 
chief source of chromite, which occurs disseminated 
in serpentinized dunite. At present substantial amounts 
of chrvsotile asbestos are mined and milled a few miles 
south of Copperopolis, where the chrvsotile occurs as 
stockworks of cross fiber veins in massive serpentine. 
Gem minerals also are associated with serpentine. In- 
cluded are jade in Mariposa County, chrysoprase in 
Amador, Mariposa, and Tulare Counties, and idocrase 
in Butte and Tulare Counties. Mariposite-bearing rock 



[ 109] 



210 



Photo 1. Diamond Springs lime- 
stone quorry. El Dorado County. 
Photo by Mary Hill. 



GfOUKJV ok NoKiniRN CaLII()RM\ 



Bull. 190 





Photo 2. Diving for gold in the 
Americon River. Phofo courfesy 
Underwater fnf erprises. 



1966 



Clark: Sierra Nevada 

r I 



211 



EXPLANAT I ON 

Gold-bearing area 

Lode gold district 

Placer gold district 

Mother Lode belt 




EXPLAf4A1 I ON 
A Asbestos 
7 Bar i te 
X Chr oini te 
• Copper 

□ Oimension stone 
■S: 6en fflinera Is 
T I ron 
IS Limestone 
s Magne« i te 
o Manganese 
A Mo lybdenun 

+ Pumice and volcanic ash 
X Pyrite 
X Sand and grave I 

S i I ica 
m Silver 
X Soapstone 
« Sulfur 
■ Tungsten 
e Uran ium 
a Zinc 
1^ Mercury 

Wol last on i te 



Figure 



Croi.()f;Y OF NoRi'HiRN Cai.iiorma 



Bull. 190 




Photo 3. Pine Creek tungsten 



associated with serpentine is a popular ornanientnl 
stone, and large quantities have been trupked to the 
metropolitan areas of the State. .\t one time consider- 
able magnesite was mined in Fresno County, and 
smaller amounts were also extracted in Tuolumne, 
Tulare, and Nevada Counties. Soapstone has been 
mined near Shingle Springs, El Dorado County, for 
many >'cars from lenses of talc schist w ith serpentine. 
Nickel has been found to be concentrated in lateritcs 
that overlie serpentine in several places, though no de- 
posits have \et been exploited. 

The production of limestone and limestone products 
is now the largest segment of the mineral industry in 
the Sierra Nevada, aniounting to lO's of millions of 



Bishop. 



dollars a \ear. Crystalline limestone and dolomite, the 
basic source rocks, occur as lenses in various t\pes of 
metamorphic rocks and granitic rock. .Mthough the 
age of most of the limestone deposits is not known, a 
few of them have \iclded fossils ranging from .Missis- 
sippian to Permian in age. The limestone usually is 
white to blue-gray in color, and fairly pure. The 
largest masses are in the Sonora-Columbia area of 
Tuolumne County, but extensive deposits are in 
Plumas, F.l Dorado, .Amador, Calaveras, Mariposa, 
Kern, and Tulare Counties. The principal districts 
producing commercial limestone at present are at 
Cool, Shingle Springs, and Diamond Springs, El Dorado 
Count)-, w here most of it is used in beet sugar refining 



1966 



Clark: Sif.rra Nf.vada 



213 




Photo 4. Argonaut gold mine at 
Jackson, Amador County. Photo by 

Mary Hill. 



or the manufacture of lime; San Andreas, Calaveras 
Count}-, where it is quarried for cement by the Cala- 
veras Cement Co.; Columbia and Sonera, Tuolumne 
County, where terrazzo stone and lime are made; and 
Tehachapi, Kern County, the site of the iMonolith 
Cement Co. operation. At one time limestone was 
quarried near Briceburg, Mariposa County, for use in 
a cement plant in A'lerced County. Wollastonite occurs 
with limestone at San Andreas and is used in cement. 

One of the largest sources of tungsten in the world 
is the Bishop district in northwestern Inyo County on 
the steep east Sierran flank. The Pine Creek mine, the 
principal property, has yielded about 1.5 million units 
of WO.-i. The ore bodies here are in a roof pendant of 
schist, hornfels, quartzite, and marble surrounded by- 
granitic rocks. Disseminated scheelite and molybdenite 
occur in garnetiferous tactite bodies, along with some 
copper minerals and gold, which are recovered as b\- 
products. Other important contact-metamorphic tung- 
sten deposits arc at the Tungstar and Tulare mines, 
Tulare County; Garnet Dike mine, Fresno Count)-; 
and the Strawberr)- mine, Aladera County. Substantial 
amounts of tungsten also have been recovered from 
the Idaho-Maryland and Union Hill gold mines at 
Grass Valley, Nevada Count\% from scheelite-rich 
quartz veins in amphibolite. 

Barite has been mined in the Sierra Nevada, the chief 
source having been the El Portal district in Mariposa 
County where nearly |3 million of barite have been 
recovered. The deposits are veinlike bodies of barite 
and witherite that have replaced limestone in slate and 
schist. Barite has also been recovered from limestone- 
replacement deposits near Alta and Graniteville, Ne- 
vada County, and Greenville in Plumas County. Many 



years ago iron was mined near Auburn in Placer 
County, where magnetite and hematite occur at the 
contact of greenstone, slate, and limestone with grano- 
diorite. The undeveloped though sizable Minarets de- 
posits in eastern Aladera County are flat-lying magne- 
tite-rich lenses in a sequence of metamorphosed 
volcanic rocks. In northern Sierra Count\- there are 
magnetite replacements of clastic sediments, tuffs, and 
dikes. 

Large quantities of sulfur were produced recently 
from the Leviathan mine in Alpine County and sent 
to Nevada for use in copper milling. This deposit con- 
sists of masses and veins of native sulfur in altered 
andesite. 

Uranium is found in a number of places, but the 
principal deposits are in the high Sierra Nevada in 
eastern Tuolumne County and upper Kern River area 
in Kern County. In eastern Tuolumne County the 
uranium occurs in black shale in a fault zone; in the 
upper Kern River region it occurs in fractures in 
granitic and metamorphic rocks, and also in Recent 
bogs. Elsewhere uranium has been found in a few 
gold and copper quartz veins, though apparently not 
in commercial amounts. 

Other important mineral commodities of the Sierra 
Nevada are lead and silver, virtually all of which have 
been recovered as a b\-product of gold and copper- 
zinc mining. Manganese is \\idespread and has been 
mined, but it is mostl\- found in small deposits in chert. 
Minor amounts of platinum occur as small grains in 
placer gold deposits. Although platinum minerals have 
not been found in place, the grains found in placers 
are believed to have been derived from the serpentin- 
ized ultrabasic rocks. Garnet, ilmenite, and zircon are 



214 



GrOUKA' OF NoRTllKRN CaI.IKORMA 



Bull. 190 



found in black sands throughout the region. Small dia- 
monds once were recovered at the Cherokee hydraulic 
mine in Butte Count)-. Minor amounts of mercury 
have been recovered west of Nashville, in El Dorado 
County, and north of Monitor, in Alpine County, 
where cinnabar is in silicified breccia in andesite. Dur- 
ing the early days of the gold rush the tellurium min- 
erals, pctzitc, calaverite, hcssite, s\lvanite, and melonite, 
were recovered in quantity at Carson Hill on the 
Mother Lode. 

The sand and gravel and stone industry- has grown 
grcath- in recent years in California as a whole and in 
the Sierra Nevada. Both Recent and Tertiary gravels 
contain large reserves. At present the principal opera- 
tions are along tlie Bear and Yuba Rivers and near 
Lake Tahoe. Crushed and broken stone of various 
types are obtained in a number of places. Rocks that 
are or have been quarried include rhyolite tuff, mar- 
ble, andesite, serpentine, granitic rocks, slate, and 



greenstone. Limestone, slate, and rhyolite tuff are 
quarried in El Dorado County for use as roofing 
granules. Quartz cobbles and massive quartz veins in 
the Mother Lode area have been mined as a source of 
silica. Some years ago quartz crystals of piczo-clectric 
grade were recovered near Mokelumne Hill in Cala- 
veras County. 

At one time the quarrying and shaping of dimen- 
sion stone was a major industrw The principal sources 
were the granite quarries of Rocklin and Penryn in 
Placer Count)-, Ra\-mond in Madera County, and 
Academy in Fresno County, and the marble quarries 
at Columbia, Tuolumne Count)-. The State capitol is 
built of Rocklin granite, while a number of public 
buildings in San Francisco and the University of Cali- 
fornia at Berkeley are of Raymond granite. Large 
bodies of andalusite-rich mica schist of potential value 
arc in western Mariposa and Madera Counties. 



REFERENCES 



Averill, C. V., 1937, Minerol resources of Plumas County: California 

Jour. Mines and Geology, v. 33, p. 79-143. 
Boteman, P. C, 1965, Geology and tungsten mineralization of the 

Bishop district: U.S. Geol. Survey Prof. Paper 470, 208 p. 
Bowen, O. E., Jr., and Groy, C. H. Jr., 1957, Mines and mineral 

deposits of Mariposa County, California: Californio Jour. Mines and 

Geology, v. 53, p. 34-343. 
Clark, W. B., and Carlson, D. W., 1956, Mines and mineral resources 

of El Dorado County, California; California Jour. Mines and Geology, 

V. 52, p. 369-591. 
Clark, W. B., and Lydon, P. A., 1962, Mines and mineral resources of 

Calaveras County, California: California Div. Mines and Geology 

County Rept. 2, 217 p. 
Ferguson, H. G., and Gannett, R. W., 1932, Gold quartz veins of the 

Alleghany district, California: U.S. Geol. Survey Prof. Paper 172, 

139 p. 



Jenkins, O. P., and others, 1948, Geologic guidebook along Highway 
49— Sierron gold belt— The Mother Lode Country; Colifornia Div. 
Mines Bull. 141, 164 p. 

Johnston, W. D., Jr., 1940, The gold quorfi veins at Gross Valley, 
California: U.S. Geol. Survey Prof. Paper 194, 101 p. 

Knopf, Adolph, 1929, The Mother Lode system of California: U.S. Geol. 
Survey Prof. Paper 157, 88 p. 

Lindgren, Woldemor, 1911, The Tertiary grovels of the Sierra Nevodo: 
U.S. Geol. Survey Prof. Paper 73, 226 p. 

Logon, C. A., 1935, Mother Lode gold belt of California: California 
Div. Mines Bull. 108, 240 p. 

Ransome, F. L., 1900, Mother Lode district, Colifornia: U.S. Geol. Sur- 
vey Geol. Atlas, Folio 63, 11 p. 

Troxel, B. W., and Morton, P. K., 1962, Mines ond minerol resources 
of Kern County: Californio Div. Mines and Geology County Rept. 1, 
370 p. 




CHAPTER V 
GREAT VALLEY PROVINCE 




Page 

217 Summary of the geology of the Great Valley, by Otto Hackel 
239 Hydrogeology and land subsidence. Great Central Valley, California, by J. F. 

Poland and R. E. Evenson 
249 Economic mineral deposits of the Great Valley, by Earl V/. Hart 



[215] 



Morysville (Suffer) Buftei. 

Sketched by Howel Willian 




[216] 



SUMMARY OF THE GEOLOGY OF THE GREAT VALLEY 



3y Otto Hacki l 
\s AND On Co., Oa 



A close association exists between physiography and 
geology in nian\' parts of California, and although 
details may vary, large contiguous areas of the State 
have distinctive features not shared bv the adjacent 
terrane. These large ph\'siographic-geologic provinces 
have been designated "geomorphic provinces" to indi- 
cate that the division has been made subject to the 
rock fabric. One of the largest and most obvious of 
these provinces in California is the Great \'alley^ — the 
topic of the following geologic summar\'. ; 

The Great Valley of California, also called the Cen- 
tral \^alle\- of California or the San Joaquin-Sacra-- 
mento \'alle\-, is a nearly flat alluvial plain extending 
from the Tehachapi Mountains on the south to the 
Klamath Mountains on the north, and from the Sierra 
Nevada on the east to the Coast Ranges on the west. 
JThe valle\- is about 4.^0 miles long and has an average 
width of about 50 miles. Elevations of the alluvial 
plain are generally just a few hundred feet above sea 
level, with extremes ranging from a few feet below 
sea level to about 1,000 feet above. The only promi- 
nent topographic eminence within the central part of 
the valley is Marysville (Sutter) Buttes, a Pliocene 
volcanic plug which rises abruptly 2,000 feet above 
the surrounding valley floor. ^ 

The northern portion of the valley is called the 
Sacramento Valley and the southern portion the San 
Joaquin X'alley. Each of these segments is drained by 
the river after which the valley has been named, and 
these, after joining about 30 miles east of San Fran- 
cisco, empty into San Francisco Bay. The southern 
extremity' of the San Joaquin \'alley, however, has 
interior drainage via the Kings and Kern Rivers into 
the depressions that in the past supported Tulare and 
Buena Vista Lakes. 

The Great Valley has been the source of about $10 
billion worth of crude oil, $2 billion worth of natural 
gas, and $1 billion worth of natural gas liquids. The 
Sacramento V^alley part has yielded tremendous 
amounts of gas but almost no oil, whereas the San 
Joaquin V^alley has yielded both oil and gas. Because 
of the differences between the two main parts of the 
Great Valley, and to some extent because of its size, 
geologists, particularly petroleum geologists, have gen- 
erally studied intensiveh" either the Sacramento or the 
San Joaquin Valley, but not both. As a result, rela- 
tively few reports on the geology of the combined 
Sacramento-San Joaquin X'alley have been published. 
In the preparation of this article a little-known com- 



prehensive report on the entire Cireat \'alle\' by C. A. 
Repenning ( I960) has been of great value, and almost 
all of the paleolithologic maps used herein are direct 
reproductions from his excellent report. 

Gcologicall\-, the Great Valley is a large elongate 
northwest-trending as\mmetric structural trough that 
has been filled with a tremendousl\' thick sequence of 
sediments ranging in age from Jurassic to Recent. This 
asymmetric geosyncline has a long stable eastern shelf 
supported by the subsurface continuation of the grani- 
tic Sierran slope and a short western flank expressed 
by the upturned edges of the basin sediments. The 
basin has a regional southward tilt, which is inter- 
rupted by two significant cross-valley faults. The 
northernmost fault, the Stockton fault, is the boundary 
used by most geologists to separate the Great \'alley 
Basin into two sub-basins, the Sacramento and San 
Joaquin. The other great cross-fault lies near the 
southern extremity of the basin and has been named 
the White Wolf fault. 

STRATIGRAPHY 

The Great Valle\- has been filled with a thick se- 
quence of sedimentary rocks of Jurassic to Recent age, 
but the locale of the thickest accumulation of sedi- 
ments varied throughout geologic time. In th© J^ti- 
ary the thickest accumulation was along the western 
edge of the southern portion of the San Joaquin basin, 
about at the present position of the structural low. 
Mesozoic rocks, however, are thickest along the west 
side of the Sacramento basin, indicating that their 
greatest deposition was probably west of the western 
edge of the present valley structural trough. It appears 
likely that a minimum of 60,000 feet of Mesozoic sedi- 
ments were laid down in the area just west of the 
present margin of the Sacramento Valley. 

The sedimentary sequence rests on a basement floor 
of nietamorphic and igneous rocks in the eastern half 
of the valley. These basement rocks, which are ex- 
posed in the Sierra Nevada foothills, are composed of 
Paleozoic and Mesozoic metasediments and volcanics 
as well as Jurassic and Cretaceous granites. Along the 
west margin of the valley, where the very thick Meso- 
zoic strata are present, basement has not been ob- 
served, either in outcrop or in well bores. Recent 
studies indicate that the terrane lying between the 
central part of the valley and the San Andreas fault 
and containing Franciscan rocks is probabl\' underlain 
by a basaltic or ultramafic basement (Baile\-, et al, 
1964). 



[217] 



218 



Gfoi.(k;v ok N'orhifrn Cai.ikorma 



Bull. 190 




.•■.■::'»i^ ■ 



1966 



Hackf.l: Great Vallky 



219 



The Jurassic, Cretaceous, and Tertiary rocks are, 
for the most part, of marine origin, though significant 
thicknesses of continental rocks are present in the 
Tertiary section. Through the entire sequence the 
rocks are almost entirel\' clastic, with siltstone, clay- 
stone, and sandstone, in that order, the dominant litho- 
logic types. E.xcept for rare occurrences, carbonate 
rocks are virtually absent. V^olcanic rocks compose 
about 10 percent of the Franciscan Formation and are 
present in minor, though important, amounts in the 
Tertiary. 

Cretaceous deposits make up the predominant for- 
mations in the Sacramento Valley, while Tertiary 
strata attain the greatest thickness in the San Joaquin 
Valley. The Cretaceous section is characterized by 
general lithologic similarities over great distances 
throughout the Great Valle\-. It is not unusual for one 
to be able to recognize at a glance Cretaceous sedi- 
ments at localities several hundred miles apart. On the 
other hand, the Tertiary strata are extremely variable 
and rock units may change facies over very short 
distances. 

The sediments that form the thick valley section 
were largely derived by erosion of land areas located 
to the east of the depositional trough. For the major 
portion of the Jurassic and Cretaceous sediments of 
the valley, the source area seems most likely to have 
been the batholiths of the Klamath Mountains and the 
Sierra Nevada. This hypothesis is based on the several 
percent of K-feldspar found in these rocks and pre- 
sumed to have been derived from the granitic rocks 
of these northern and eastern highlands (Bailey and 
Irwin, 1959). The lack of K-feldspar in the valley 
(east of the San Andreas fault) Franciscan Formation 
either indicates a different source area or that most 
of this formation predates the unroofing of the batho- 
liths (Bailey and others, 1964). There is evidence to 
indicate that the Diablo Range was a periodically 
emergent land mass during later parts of the Late 
Cretaceous and that this area contributed sediments 
to the Late Cretaceous sea. The arkosic nature of the 
Tertiary sediments seems to indicate the principal 
source area was probably the elevated granitic batho- 
liths of the Sierra Nevada and Tehachapi Mountains. 
Coarse arkosic sediments in the upper Miocene of the 
western San Joaquin basin, however, may indicate a 
granitic source area then existed west of the town of 
Fellows. Other localized areas in the Coast Ranges 
probably contributed debris into the Tertiary seas. 

The Mesozoic basin of deposition covered a greater 
area than just the Great V^alley trough, as Jurassic 
and Cretaceous rocks are either exposed in or underlie 
large portions of the region between the valley and 
the Pacific Ocean. In contrast, the Tertiary basins 
were much more restricted and distinct; they had 
relatively narrow and limited connections to the open 
western sea. 



Pre-Uppermost Jurassic Rocks 

Except along the west side. Paleozoic and other pre- 
uppermost Jurassic (pre-Tithonian) rocks are exposed 
on the highlands along the edges of the Great X'alley. 
These rocks appear to have been uplifted and region- 
ally metamorphosed near the close of the Jurassic 
with accompanying intrusion of granitic batholiths. 
Such rocks have been described from outcrops north 
of the Great X'allev in the Redding and Taylorsville 
area, as well as all along the Sierra Nevada. Exotic 
blocks of marble and other metamorphic rocks of 
undetermined age in the San Emigdio Mountains, and 
in the Temblor Range w est of Fellows, may indicate 
such rocks were formerh' also exposed south and 
southwest of the valley. 

Uppermost Jurassic Rocks 

Recent geologic studies of the Upper Jurassic and 
Cretaceous rocks of the Great \'alie\' and environs has 
led to the conclusion that two entirel_\' different suites 
of rocks were deposited at the same time in closely 
adjoining areas (Irwin, 1957). These two units are the 
Franciscan assemblage and the thick sequence of 
equivalent clastic rocks that are best exposed along 
the western edge of the Great \'alley. Both the 
Franciscan and the Great X'alley sequence have been 
proven through fossil evidence to range from Late 
Jurassic to Late Cretaceous. Consequenth-, it now ap- 
pears that any discussion of the stratigraphy of the 
Great Valley must include the Franciscan not as "base- 
ment," but as a eugeosynclinal facies of the miogeo- 
synclinal Great V^alley sequence. 

Franciscan Formation 

The assemblage of rocks generally referred to as 
Franciscan is widely scattered throughout the west 
side of the Great \'alley from Paskenta south to Park- 
field. Isolated intrusions of ultrabasic rocks carrying 
Franciscan inclusions are present as far south as Cedar 
Canyon at the S'/4 cor. T. 27 S., R. 18 E. This is 
the southernmost occurrence of Franciscan east of the 
San Andreas fault, and it is interesting that this locale 
is nearly as far south as the southward extent of the 
Great Valley sequence on the west side of the San 
Joaquin \'alle\'. The two sequences seem to go hand 
in hand. 

The Franciscan comprises a thick sequence of gray- 
wacke, dark shale, volcanic rocks of submarine origin 
(pillow lavas), chert, limestone, and some metamor- 
phic rocks containing minerals of the-glaucophane or 
blueschist facies. Serpentinites are commonly associ- 
ated with the Franciscan rocks but are excluded from 
the formation because they appear to be intrusions. 
The above ma\- appear from the description to be a 
heterogeneous assemblage, but it is so typical and 
distinct that most of the Franciscan outcrops are 
readih- recognizable as such. 

The base of the Franciscan has never been seen, but 
it has been inferred that the formation lies on an ultra- 
mafic (peridotite) basement. The top of the formation 



220 



(7i()I.ck;y ok Norhiirn Cai.ikorma 



Bull. IW 



is also subject to ijucstion and has not been adequatcl\' 
defined. Tlic contact betw ccn the Franciscan and the 
Great \'allc\ sequence, where exposed, is al\va\s a 
fault so that the relationship between these major units 
is also difficult to deduce. 

The thickness of the Franciscan cannot be calcu- 
lated b\- an\- coincntional stratigrapliic means owing 
to its great deformation as well as to the lack of a 
known base or top. Adding tiiicknesses of sections 
that are thought to liavc been deposited at different 
times leads one to conclude that a minimum thickness 
of about 5(),0()() feet was deposited (Bailey and others, 
1964). 

The fossils that have been found in the Franciscan 
give a range in age of from Late Jurassic to Late Cre- 
taceous. Megafossils are ver\- rare, but Foraminifera in 
limestone and Radiolaria in chert are locall\' abundant. 
it is unfortunate that the limestones with their diag- 
nostic microfossils are so small a part of the Franciscan 
that a great deal of the formation cannot be dated 
b\' this means. 

The source of most of the Franciscan along the 
west side of the Great X'allcy appears not to have been 
the same (Klamath Mountains and Sierra Nevada) as 
that of the Great \'alle\- sequence because of the lack 
of K-feldspar and lithologic dissimilarity of the rocks. 
It appears likel\- that, except for older pre-Knoxville 
Franciscan rocks, the source area was to the west or 
even from cannibalism of older Franciscan exposures. 
This latter source area during the Late Upper Creta- 
ceous ma\" have been the emergent central part of the 
Diablo Range, as shown by a stratigraphic hiatus in 
the Great V'alley sequence in this area. 

Knoxville Formation 

The oldest known unit that can be considered to 
be a part of the Cireat \'alle\' sedimentar\' sequence is 
the Knoxville Formation of the Late Jurassic age. The 
Knoxville, as a formational unit, is based mainly on 
faunal rather than lithic criteria and most commonly 
refers to the beds containing the Late Jurassic Eiichia 
piochii (White, 1H85, p. 19). 

The Knoxville crops out along the west side of the 
Sacramento X'allev from just north of Mount Diablo 
northward to bcx'ond Paskenta to the Elder Creek 
fault zone. Its eastern limit is buried in the X'alley be- 
neath \-ounger rocks. On the west side of the San 
Joaquin X'aliey several areas contain limited outcrops 
of rocks that iiave been assigned to the Knoxville be- 
cause of their fossil content. Such areas are found in 
the Tesla, Paciieco Pass, Priest \'alle\-, and Panoche 
quadrangles, in the Orchard Peak area, and southward 
along the crest of the Temblor Range between Bitter- 
water and Salt Creeks. In these latter areas, however, 
the Jurassic fossils are cither mixed with Cretaceous 
assemblages or the rocks have been so inadequately 
studied that stratigraphic conclusions are not certain. 

Lithologically, the Knoxville includes all varieties of 
clastic rocks ranging from sliale to conglomerate, but 



dark-gra\- to black hackl\ fracturing shale or mud- 
stone predominates. .Massive lenticular conglomerates 
up to several thousand feet thick are erratically dis- 
tributed in the mudstone. The sandstones are dark 
gray and of the graxwacke t\pc. The lower part of 
the section in some places contains volcanic flows, tuff 
beds, and chert. 

The thickest sections of the Knoxville are in the 
Sacramento \'allc\-, w here south of Paskenta it is about 
20,000 feet thick. In other places the preserved Knox- 
ville section is less, but as the basal contacts are usu- 
all>' faults it is difficult to determine whether there 
was actually reduced sedimentation in a southward 
direction. 

The basal contact of the Knoxville is invariably 
faulted against Franciscan or associated rocks. In most 
areas the upper contact with overlying Cretaceous 
rocks is gradational with similar lithologies above and 
below . .At the north end of the Sacramento \'alle>% 
however, buried Knoxville rocks arc presumed to be 
overlapped h\- Lower Cretaceous strata that in outcrop 
rest on basement. 

The depositional environment of the Upper Jurassic 
rocks was marine but of fairl\- shallow water, and the 
limited faunas suggest a turbid, brackish or very cold 
water ecologic condition. The source of the sediments 
was apparently from the Klamath Mountains to the 
north and the Sierra Nevada to the east. 

The Knoxville fauna includes common Biicbias 
(= Aiicelln), scattered belemnitcs and ammonites, and 
rare Foraminifera. The index fossil is Biicbia piochii. 

Cretaceous Rocks 

Miogeos\nclinal Cretaceous rocks are present 
throughout the Great X'alley as far south as western 
Kern County. The Early Cretaceous sediments have 
commonh" been assigned to the Shasta Series and Late 
Cretaceous rocks to the Chico Group. As a rule, litho- 
logic similarities throughout the section have made di- 
vision into formations difficult so that the separation 
of the Cretaceous rocks into the Shasta Series and 
Chico Group has been based mainly on faunal rather 
than lithologic criteria. Except for areas of limited 
extent, the most commonl\- used subdivisions in the 
subsurface are also based on faunal content. 

Lower Cretaceous (Shasta) Rocks 

Lower Cretaceous rocks are widel\- exposed along 
the western margin of the Great \'alle_y, but the>' do 
not extend to the eastern side. The distribution of 
these rocks in the Sacramento \'alle>' is fairly well 
documented but in the San Joaquin \'alle>' they have 
not been as thoroughl\- studied. Tiie apparent absence, 
near the base, of faunal zones found elsewhere in this 
interval, has led some geologists to place an uncon- 
formity at the lower boundary of the series, but the 
generally unfossiliferous character of the lower hun- 
dreds of feet of strata could account for this discrep- 



1966 



Hackki,: Gki ,\i \'ai,i,i.y 



221 




Figure 2. Distribution and thickness of Cretac 
Repenning (1960, fig. 4). 



sediments in the Great Valley at the beginning of Tertiary time. After 



GlOLOGY OF NORTHKRN CaLIKORMA 



Bull. 190 



anc>' cijuallv w cli. The consensus of geologists now is 
that the Lower Cretaceous rocks are conformable at 
their base with the Knoxville and also at their upper 
contact uith the Chico, except locally at the margins 
of the depositional basin where Upper Cretaceous 
rocks overlap the older units. 

The Lower Cretaceous Shasta Series consists of over 
20,000 feet of mudstone, siltstone, conglomerate, gra\- 
wacke, and minor limestone. The mudstones cover 
large areas and are the dominant rock type. The gra\- 
wacke sandstones occur in limited amounts, whereas 
the conglomerates attain great thicknesses but arc very 
lenticular. In parts of the section the mudstones and 
sandstones are rh\tiimicall\- interbedded, and the sand- 
stones exhibit graded bedding indicative of deposition 
by turbidity currents. 

The Lower Cretaceous .sediments locally contain a 
moderately abundant and diversified megafossil fauna. 
Although ammonites are generallx' uncommon, with 
the help of pelec\pods ever\- stage of the Lower Cre- 
taceous has been identified. Foraminifera occur 
throughout the section but are most numerous in the 
upper portion w here some attempts to use them for 
zoning have been made. 

The distribution of the megafossils, with man\' more 
in the northern area, indicates that the depositional 
environment for the Lew er Cretaceous rocks was shal- 
lower in the north portion of the Great \'alley than 
in other areas of outcrop. Farther south the predomi- 
nant fine clastic litholog\' and the abundance of tur- 
bidities points to deposition below wave base for most 
of the section. One exception to this is the unusually 
great a real extent of the Biichia crassicolUs fauna, 
which is ubiquitous in coarse sandstones or massive 
conglomerates near the base of the Lower Cretaceous. 
In the Sacramento \'alle\' the coarser elastics to the 
north have been cited as an indication that the sedi- 
ments were derived from a source area to the north 
or the northeast. 

Upper Cretaceous (Chico) Rocks 

Upper Cretaceous rocks are much more widespread 
than the previously described older Mcsozoic units. 
The>' crop out throughout the west side of the Sac- 
ramento \'alley and extend eastward beneath younger 
rocks in the valle\- to exposures in the eastern foothills 
where they are much thinner. The t\pe Chico area 
on the east side of the Sacramento \'alley represents 
only a small part of the Upper Cretaceous exposed 
on the west side. In the San Joaquin \'alley, the Upper 
Cretaceous rocks crop out through the length of the 
Diablo Range and extend southward into the north- 
ern Temblor Range. 

The Upper Cretaceous rocks have been studied in 
many areas in recent years, and man\- formations, 
members, and faunal zones have been described and 
named. In the Sacramento \'alley, Kirb\- (1943) di- 
vided the upper part of the Upper Cretaceous strata 
exposed on the west side from Putah Creek in Yolo 



County to Logan Creek in Glenn County into six for- 
mations. At the northwest end of the Sacramento 
X'alley, Murphy and Rodda (1960) described the Bald 
Hills Formation. In the northern San Joaquin \'alley, 
from .Mount Diablo southward to Coalinga, the Upper 
Cretaceous rocks have been subdivided into the Pan- 
oche and Moreno Formations. Further subdivision is 
made in the Coalinga area where two prominent sand- 
stt)nc members separated by a shale in the Panoche 
ha\e been named in descending order the Brown 
.Mountain Sandstone, Ragged X'alley Shale, and Joa- 
quin Ridge Sandstone. 

GoudkofF (1945) subdivided the Upper Cretaceous 
rocks into several microfaunal zones lettered from A 
to H. These zones have been wideK' accepted as work- 
ing units by most geologists dealing with the Creta- 
ceous of the Great \'alle\-, and thev provide the basis 
for most subsurface correlations. Other Upper Creta- 
ceous units, however, have been informally- named b\- 
geologists working with well bore information in par- 
ticular areas, and several of these units that are now 
w idel\' known and used should be formally described 
and named. These units have such names as Dobbins 
Shale, Sacramento Shale, Lathrop Sand, Winters Sand, 
TracN' Sand, Starkex' Sand, Delta Shale, Garzas Sand, 
Kionc Sand and others. 

The most distinct lithologic break present in rocks 
exposed along the west side of the Sacramento \'alle\- 
separates the lower and upper, portions of the Upper 
Cretaceous strata rather than the Lower and Upper 
Cretaceous beds. The sediments of the lower Upper 
Cretaceous are lithologicall\" more like the Lower Cre- 
taceous than the overlying Upper Cretaceous beds. 
Beds that represent the lower part of the Upper Cre- 
taceous can be readil\- separated and mapped as a unit 
throughout Colusa, Glenn, Tehama, and Shasta Coun- 
ties, but south of Colusa County there is no apparent 
distinction between beds assigned to the lower part 
of the Upper Cretaceous and those belonging to the 
Lower Cretaceous. In southern Colusa County, the 
lower Upper Cretaceous is thickest (about 6,500 feet) 
and it thins northward. Northeast of Ono in Shasta 
County it is completely- overlapped by the upper 
Upper Cretaceous strata. As is the case in the Lower 
Cretaceous, sandstones and conglomerates are impor- 
tant components in the north and shale is predominant 
to the south. However, in Colusa County, a persistent 
conglomerate, the "Salt Creek" Conglomerate (Den- 
nings, 1954), marks the ba.se of the lower Upper Cre- 
taceous. Similar though discontinuous conglomerates 
are found more or less at the same stratigraphic level 
at the north end of the valle\-. These conglomerates 
carry reworked Lower Cretaceous clasts, which is in- 
terpreted by some geologists as indicating a period of 
uplift and erosion in local marginal areas at the end 
of the Lower Cretaceous. 

An upper, major, part of the Upper Cretaceous on 
the west side of the Sacramento Valley has been well 



1966 



Hackf.l: Crfat N'^allf.y 



223 



» 



described by Kiil)\-, whose f ormation^the , \'enado, 
Yolo, Sites, Funks, Cuinda and Forbes — were depos- 
ited duTmg this period. Alternations of sandstone with 
siltstone and shale comprise these formations, with tiie 
finer elastics being siightl\' predominant. Conglomer- 
ates are much less abundant than in the underlying 
older Cretaceous sequence, and most of those present 
are in the lowermost unit, the \'enado Formation. 
Eastward across the Sacramento \'alley equivalents of 
the \^enado, Yolo, and Sites Formations are overlapped 
by the younger formations. No rocks older than 
Venado have been penetrated by wells in the alluvi- 
ated portion of the Sacramento Valley, and no beds 
younger than Forbes crop out, e.xcept at the extreme 
, southern end. The thickest section of strata assigned 
to the upper part of the Upper Cretaceous is along 
Putah Creek, on the Solano-Yolo County line, where 
1 .'i,000 feet are present. Most of the gas produced in 
the fields recenth- discovered in the central and west 
side of the Sacramento Valley comes from lenticular 
sands equivalent in part to the Forbes Formation. 

In the San Joaquin Valley, the Panoche Formation 
of the type locality (Panoche Hills-Fresno County) 
has been subdivided into six formations bv Payne 
(1962). His subdivisions in ascending order are the 
Redil, Benito, Ciervo, Marlife, Television, and Uhalde 
Formations. They are composed of shale, sandstone, 
and conglomerate, \\'ith shale predominating, and they 
attain an aggregate thickness of over 22,000 feet. The 
overlying Moreno Formation consists of about 3,000 
feet of interbedded organic shale and fine-grained 
sandstone, with a sand-shale ratio about 0.12. The 
contact between the Cretaceous and Tertiary rocks 
is gradational and has been placed within the Moreno. 

The southernmost occurrence of Upper Cretaceous 
rocks in the Great V^allev is at the headwaters of Salt 
Creek in the SE'/4 of T. 29 S., R. 20 E., in western 
Kern County, where there are e.xposed interbedded 
shale and sandstone strata assigned by Dibblee ( 1962a) 
to the Panoche. At this point the Panoche is over- 
lapped from the south b\- Tertiar\- beds, and its south- 
ward subsurface continuation is not known. 

Source areas for the Upper Cretaceous rocks in the 
northern Sacramento Valley have not been positively 
identified, but the Klamath Mountains and Sierra Ne- 
vada are the most likely sources. Undoubtedly the 
Sierra Nevada also contributed substantially to the 
sediments deposited during Late Cretaceous time in 
the southern Sacramento \'alley and the northern San 
Joaquin \^alley, but studies of sand distribution in the 
subsurface of these areas indicate that a western source 
also existed during certain periods (Callawa\-, 1964; 
Hoffman, 1964). The strongest evidence for a western 
source is the fact that thick sand bodies appear to 
change facies to shale in an east\\ard direction. Parallel 
studies of the clasts and detritus in the west side out- 
crops have not been definitive enough to establish 
either a western or eastern source. 



Tertiary Rocks 

Kp> Development of the general form of the Tertiary 
basins began with tectonic movements near the close 
of the Late Cretaceous Period. These movements ele- 
vated many Coast Range areas, including the Diablo 
Range adjacent to the northern San Joaquin \'allev 
and the larger regional uplift along the entire west 
side of the Sacramento X'alley. The ancestral Terti- 
ar\- San Joaquin and Sacramento Basins were thereby 
brought into being as restricted troughs of deposition 
lying bet\\ecn the uplifted western Coast Ranges and 
the eastern Sierra Nevada landmass. In these troughs 
marine and continental deposition took place through- 
out the Tertiary Period. 

Tertiar\- rocks, ranging in age from Paleocenc to 
Pliocene and of both marine and continental origin, 
w ere continuously deposited at one place or another 
in the Great Valle\-. The greatest accumulation of 
these strata is in the southern San Joaquin \'alley, 
where they are more than 35,000 feet thick. In the 
Sacramento \'allev at least 12,000 feet of Tcrtiar)- 
rocks occur in the soutiiern part, or Delta area. These 
points of greatest accumulation, and their relation- 
ships, indicate that the Tertiary marine rocks were 
laid down in r«o separate basins. These basins, the 
San Joaquin and the Sacramento, were separated by a 
faulted trans-valle\' Cretaceous high called the Stock- 
ton Arch (Hoots and others, 1954). Northward to- 
ward this Stockton Arch the lower Tertiary marine 
sediments of the San Joaquin Basin appear to thin and 
in the vicinity of Modesto the\' are truncated by over- 
l\'ing continental sediments. Because of this truncation 
one cannot determine whether lower Tertiar\' sedi- 
ments were deposited and later eroded from the Stock- 
ton Arch or were never deposited there. On the north 
side of the arch a thick section of marine Tertiary 
sediments abuts the large fault which marks the north 
edge of the arch (Am. Assoc. Pet. Geologists, 1958, 
no. 10), indicating its crest during the lower Tertiary 
deposition was not in its present position near Stock- 
ton but farther south in the vicinity of Modesto. In 
the Sacramento Basin the Tertiar\' marine section also 
thins northward and is overlapped b\' Pliocene con- 
tinental sediments north of Chico. 

The depositional history in the Great \'alley during 
the Tertiary was very complex. Rapid lateral changes 
in thickness and lithology are common, and as a result 
a large number of units have been named, both for- 
mally and informally. 

Paleocene Rocks 

Rocks of Paleocene age are present in both the 
northern San Joaquin \'alle\' and in the southern 
Sacramento \'alle\'. In both areas deposition appears 
to have been continuous from Cretaceous into Paleo- 
cene time, and time boundaries do not necessarily co- 
incide with lithologic boundaries. 

Formations in the San Joaquin \'alley which have 
been assigned to the Paleocene include the upper part 



224 



Gf.()i,o<;v ok Northkrn Cai.ikokma 



Bull. 190 



EXPLANATION 



MARINE 
DEPOSITS 



CONTINENTAL 
DEPOSITS 



HEAVY LINE SHOWS PRESENT LIMITS OF 
SEDIMENTARY ROCKS IN THE CENTRAL VALLE1 



SCALE IN MILES 
10 JO SO 




SOURCES 

NORTH OF STOCKTON ARCH-- 

Several sources but information 

very approximate 
SOUTH OF STOCKTON ARCH-- 

Hoots, Bear, and Kleinpell, 1954a, 

with slight addition. 



Figure 3. Distribution and thicknels of Poleocene and lower Eocene sediments in the Greot Volley ot the beginning of lote 
Eocene time. After Repenning (1960, fig. 5). 



1966 



Hackil: Grkat Vai.lf.y 



225 



of the Moreno, the Laguna Seca, the lower portion 
of the Lodo, the Dos Palos, and the Weyant sand of 
the Hehn oil field. The\- are best developed along the 
west side of the \'alle> north of Coalinga. However, 
in the southern San Joaquin Valley, Paleocene rocks 
seem to be absent and probably they do not extend 
south of a line drawn between Coalinga and Hanford. 
Toward the Stockton Arch in the vicinity of Modesto, 
Paleocene rocks are truncated by the overlying Mio- 
cene-Pliocene continental beds (Hoffmann, 1964). 
Eastward from the central part of the valley the Paleo- 
cene units are truncated by the significant unconform- 
it\' at the base of upper Eocene. 

In the southern Sacramento \"alle\- the Paleocene 
is represented by the Alartinez Formation and the 
lower portion of the Meganos Formation. The type 
iVIartinez contains rocks \ounger than those consid- 
ered to be of Paleocene age, but in outcrop in other 
areas and in the subsurface it has been restricted to the 
Paleocene. The Martinez pinches out in exposures 
south of iMount Diablo, but is present in the subsurface 
to the east and north. At the type section it consists 
of 2,000 feet of silty cla\stone with thin interbeds of 
sandstone and conglomerate. The younger Paleocene 
rocks generally are assigned to the lower part of the 
Meganos Formation, which is dominantly sand with 
shale interbeds. iMeganos sediments fill a meandering 
channel or gorge several hundred feet deep, which 
has been found by drilling and other methods to ex- 
tend from the vicinit\' of the Thornton gas field (Sil- 
cox, 1962) westward through the Brentwood oil field. 

Recognition of Paleocene strata in many places de- 
pends solely on faunal content. In some areas of out- 
crop megafossils have been used, but in the subsurface 
Foraminifera are most useful. Laiming (1943) subdi- 
vided the Eocene (including the Paleocene) into 
faunal zones lettered A through E, with the Paleo- 
cene section forming his D and E zones. 



Eocene rocks of both marine and continental facies 1 
are widespread throughout the Great V^alley. The 
thickest deposition took place along the \\ estern mar- 
gin of the basin with greatest accumulation in the 
Delta area of the Sacramento \'alley and at Devils Den 
in the San Joaquin Valle\'. Sand distribution patterns 
suggest that source areas for the Eocene sediments 
were highlands lying on all sides of the basin. 

Lozcer Eocene Rocks. Lower Eocene rocks in the 
Sacramento Valley are assigned to the Capay Forma- 
tion and the upper part of the Meganos Fomiation; 
in the San Joaquin \'alle>- they are assigned to the 
upper part of the Lodo Formation and to the Yokut 
Sandstone. South of Mount Diablo, Huey (1948) has 
described the Tesla Formation and assigned it to the 
lower Eocene. As is the case with the Paleocene, no 
lower Eocene rocks are present in the southern San 
Joaquin \^alley. 



In the Sacramento Valley lower Eocene rocks are 
exposed along the west side as far north as Chico. 
In the central Sacramento \'alle\' the Itjwer Eocene is 
buried, but is knov\n to be largely confined to a deep 
narrow subsurface gorge \\ hich has been named the 
"Capay Gorge" (Repenning, 1960) or "Princeton 
Gorge" (Am. Assoc. Pet. Geologists, 1960, no. 13; 
Safonov, 1962). Although most of the lower Eocene 
rocks of the Sacramento V'alley are referred to the 
Capa\' Formation, some in the Mount Diablo area and 
in the nearb\- suljsurface are assigned to the upper 
part of the Meganos. The Capay Formation, and the 
portion of the Meganos assigned to the lower Eocene, 
is composed of dark shale, which appears to have been 
deposited in a basin w ith stagnant bottom conditions. 
In general, the Capa\' thickens w estw ard, but through- 
out most of the southern Sacramento \"alley it has a 
rather uniform thickness of 300 to 400 feet. At the 
type locality, however, it is about 2,500 feet thick, and 
it fills the "Capay Gorge" to depths of 2,000 feet. 

Lower Eocene strata are discontinuous across the 
Stockton Arch, but south of it lies the Lodo Forma- 
tion that is similar lithologicall\' to the Capay but w ith 
a much larger content of sand and fewer features 
suggesting stagnant marine conditions. These differ- 
ences suggest that the Stockton Arch acted as a bar- 
rier between tw o basins of deposition during the early 
Eocene. 

In the San Joaquin Valley the lower Eocene was 
deposited as far south as the Bakersfield Arch, but is 
not found south of it (Hoots and others, 1954). Depo- 
sition began with the Lodo Formation, w hich has been 
subdivided into the lower Cerros Shale, the intermedi- 
ate Cantua Sandstone, and the upper Arroyo Hondo 
Shale. The Lodo has a maximum thickness of 5,000 
feet in the west side outcrops but in many areas is 
less than 1,000 feet thick. In going eastward the Lodo 
Formation pinches out by thinning from the bottom 
and truncation at the top. The Yokut Sandstone over- 
lies the Lodo Formation along the western side of the 
San Joaquin Valley between Coalinga and the Panoche 
Hills. In outcrop it is usually about 200 feet thick, 
but it is thicker to the east and south where in the 
subsurface it is known as the Gatchell Sand. 

The Tesla Formation where exposed along the w est- 
ern edge of the northern San Joaquin \'alle\- attains 
a thickness of 2,000 feet. It is predominantly a sand- 
stone unit and contains megafossils indicating it is 
equivalent in age to the Lodo and Yokut. Just south 
of Mount Diablo it is overlapped by .Miocene units. 

Minor amounts of continental sediments may have 
been deposited at this time in the eastern San Joaquin 
\'alle\- forming the low er part of the \\'alker Forma- 
tion, and in the northern Sacramento \'alle>' forming 
the Montgomery Creek Formation. 

The early Eocene closed with a marked regression 
of the sea that resulted from uplifts along the margins 
of the Great \'allc\- and from elevation and folding 



226 



Ckoi.(x;v ok NoRiiiiKN Cm.iiormx 



Bull. 190 



EXPLANATION 



MARINE 
DEPOSITS 



CONTINENTAL 
DEPOSITS 



HEAVY LINE SHOWS PKESENT LIMITS OF 
SEDIMENTARY ROCKS IN THE CENTRAL VALLEY 



-itf^ 




SOURCES 
NORTH OF STOCKTON ARCH— 

Several sources but information 

approximate. 
SOUTH OF STOCKTON ARCH— 

Hoots, Bear, and Kleinpeil, 1954a, 
with some change. 






Figure 4. Distribution and thickness of upper Eocene sediments in the Greot Valley ot the beginning of Oligocene time. 
After Repenning (1960, fig. 6). 



1966 



Hacki L: Grfat Vali.ky 



227 



of some previously submerged basin areas in the 
valley. 

Upper Eocene Rocks. Regional subsidence at the 
beginning of late Eocene time brought about an exten- 
sive marine transgression in the San Joaquin \'alle\ 
and to a lesser extent in the Sacramento \'alley, form- 
ing a significant unconformit\- betw een the lo\\er and 
upper Eocene. In the San Joaquin \'alley, this uncon- 
formity is at the base of the Domengine Sandstone, 
or beneath younger units that overlap the Domengine 
at the margin of the basin. In the Sacramento V'al- 
ley, the unconformity is also present at the base of 
Domengine in the Delta area and is at the base of the 
lone Formation to the north and east. 

In the San Joaquin Valley the upper Eocene rocks 
comprise a fairl\' complete cycle of basin deposition, 
and the different cycles and lithologic facies in dif- 
ferent areas have received numerous names. The earli- 
est transgression of the late Eocene sea deposited in 
the northern San Joaquin Valley a grittv or con- 
glomeratic sandstone called the Domengine Formation, 
and at about the same time in the area south of Bakers- 
field the Uvas Conglomerate Member of the Tejon 
Formation was deposited. Well bore data suggest that 
the Domengine and the older portion of the Tejon 
were separated in the vicinity of Bakersfield b\' a bar- 
rier — the Bakersfield Arch (Hoots and others, 1954). 
Subsequent Eocene deposition covered the Bakersfield 
Arch, but differences between the Tejon fauna and 
the Kreyenhagen fauna in rocks farther north indicate 
that the depositional environment north and south of 
the Arch was not the same. The Tejon Formation at 
the south end of the valley consists of 2,. 500 to 4,000 
feet of sandstone, siltstone, and clay shale believed to 
have been derived from the nearby San Emigdio and 
Tehachapi Mountains still farther south. At the same 
time farther north and west in the San Joaquin Valley 
the Domengine, Canoas, Point of Rocks and Kreyen- 
hagen Formations were deposited. The Domengine is 
quite variable in thickness, ranging from a few feet 
of "grit zone" to 1,000 feet of strata in the .Mount 
Diablo area. An equivalent of the Domengine found 
in the Kettleman Hills area is the thick (1,000± feet) 
Avenal Sandstone. The Canoas consists predominant!}- 
of clay shale and in certain areas, such as Devils Den, 
it contains sand lenses of significant thickness. Over- 
lying the Canoas is the Point of Rocks Sand, which 
has a maximum of several thousand feet. The Kre\en- 
hagen Formation consists of a thick and widespread 
sequence of shale which crops out along the western 
side of the San Joaquin \'alle\' from south of Pacheco 
Pass to the vicinity of Devils Den. It extends in the 
subsurface southward and eastward towards the cen- 
tral part of the basin. The Kreyenhagen, Point of 
Rocks, and Canoas, are in realit)- depositional facies of 
one another laid down in different environments dur- 
ing the upper Eocene. Farther east these marine units 
change facies to a near-shore deposit known as the 



Famosa Sand, which, in turn, grades still farther east- 
ward into nonmarinc clavs and sands that have been 
included in the Walker Formation. The Walker, how- 
ever, encompasses more than just Eocene sediments, 
as the term has been used to include nonmarine sedi- 
ments of Eocene to early Miocene age along the east 
side of the southern San Joaquin Basin (Rudel, 1965). 
The Kreyenhagen becomes sandier to the north and 
is correlative with the Nortonville and Markle\- For- 
mations of the Mount Diablo area. 

In the Sacramento Valle>' the oldest upper Eocene 
rocks are represented by the lone Formation, which 
is present throughout the central part of the valley. 
In most places the lone is an unusual nearly massive 
quartzose sand with a high percentage of interstitial 
cla\-, but a shale which overlies the sand in the center 
of the basin is generally also assigned to the lone. The 
formation throughout most of the area is about 200 
feet thick, although near Mount Diablo an lone equiv- 
alent, which lies in the Domengine, is about 500 feet 
thick. The lone grades northeastward into the Buttd 
Gravels, which overlie the granitic basement along th^ 
eastern edge of the valle\-. Throughout the central ana^ 
northern part of the Sacramento \'alley the lone rep- / 
resents the last marine invasion, and it is unconform- 
abl\- overlain by Oligocene or Miocene volcanic rocks 
or nonmarine Pliocene sediments. In the southern part 
of the Sacramento Valle\-, however, \ounger Eocene 
rocks are marine and include, in ascending order, the 
Domengine, Nortonville, and Markley Formation. The 
Domengine Formation in outcrop along the north side 
of Mount Diablo is about 1,000 feet thick and consists 
of a lower shale and coal unit, 500 feet of sandstone 
called "lone," and 800 feet of upper shaly brown sand- 
stone. In the subsurface of the Delta area, in the south- 
ern Sacramento Valley, the lower unit varies in thick- 
ness and character but the typical white of the "lone" 
sand and brown (greenish in subsurface) of the upper 
sandstone are prominent. Towards the eastern margin 
of the basin the Domengine thins and the units lose 
their individual character. The younger iMarkley For- 
mation on the north flank of Mount Diablo is com- 
posed of a lower 2,000-foot sandstone member, a 700- 
foot shale unit, and an upper 500-foot sandstone. The 
intermediate shale unit has been correlated with the 
Krevenhagen Shale of the San Joaquin \'alley. The 
ba.sal unit of the Markley has been called the Norton- 
ville Formation, and in the subsurface of the southern 
Sacramento X'alley this is a relativel\- widespread unit 
of marine shale localK' containing thin sand>- beds. .\ 
well-documented buried channel — the Markle\- Gorge 
— filled with upper Eocene and Oligocene sediments 
extends in the subsurface from southeast of Marysville 
beneath Sacramento and continues to the south to- 
wards the Rio Vista Gas Field. (Almgren and Schlax, 
1957; Safonov, 1962). To the north up the regional 
gradient of the Sacramento X'alley, the channel cuts 
down into the Upper Cretaceous Starke\- Sand but in 



228 



Croitxi's or NoKiiiiRs (^mhokmv 



Bull. \W 




SOURCES 

NORTH OF STOCKTON- - 
Several sources. 

SOUTH OF STOCK TON — 

Hoots, Bear, and Kleinpell, 1954a, 
with considerable revision 



Figure 5. Distribution and thickness of Oligocene sediments in the Great Valley at the beginning of Miocene tii 
Repenning (I960, fig. 7). 



1966 



Hackf.l: Grkat \'allky 



229 




2?0 



Ci:()i.(x;y of N'orthihn Caliiorma 



Hull. 190 



the vicinit\- of Rio Vista it onl\ brcaclics the Capa> 
Shale. 

Oligocene Rocks 

Regional uplift at the close of Focene time affected 
the basin areas of the Great \'alley, with the result 
that Oligocene marine deposits are thinner and more 
restricted in extent than the Eocene marine rocks. 

Oligocene rocks in the San Joaquin \'alle>' iacludcs 
such marine units as the Tumey Shale (including in 
certain areas the upper part of the Krevenhagen Shale) 
the Oceanic Sand, tiie San P'migdio Formation and a 
portion of the Plcito Formation. Continental deposits 
are represented l)\- the Tecu\'a and the Walker Forma- 
tions. The Tume> Shale is present along the western 
and central parts of the San Joa(]uin X'alley from the 
Panoche Hills southward to the Bakcrsfield Arch, and 
along the west side it includes a basal sandstone which 
crops out north of Coalinga. Farther south, in the 
subsurface between Devils Den and McKittrick, a 
basal sand that has been termed the Oceafiic Sand is 
present. South of the Bakersfield Arch the predomi- 
nantly marine sandstone and siltstone of the San 
Emigdio Formation and the lower part of the Pleito 
Formation were deposited near the present base of the 
San Emigdio Mountains. At the southeastern e.\tremit\' 
of the \'alle\' a series of continental deposits was laid 
down in late Oligocene and early Miocene time^ — these 
rocks have been named the Tecu>'a Formation. Similar 
continental rocks, known as the Walker Formation, 
were deposited farther north along the east side of the 
San Joaquin \'alle\'. 

In the Sacramento \'alle\-, Oligocene rocks are rep- 
resented b\' the Kirker Formation along the western 
margin, and possibly by the Wheatland Formation 
along the southeastern margin. The San Ramon Sand- 
stone of the Berkele\' Hills is of the same age. The 
Kirker Formation, which was described in the area 
north of .Mount Diablo, consists of 400 feet of sand- 
stone and tuff resting unconformabl\' on underlying 
rocks. \'er\' little is known of the subsurface distri- 
bution as the available infor^iiation is inadequate to 
separate it from younger continental sediments lying 
on it. The .Markle>' Ciorgc in the subsurface of the 
Sacramento \'alle\' has been reported to contain ma- 
rine Oligocene .sediments as well as upper Eocene 
strata. 

In nearly all parts of the Great N'alley an erosional 
unconformit\ separates Oligocene or older units from 
the overlying Miocene rocks. In the southern San Joa- 
quin \'alle_\-, especiall)- in the basinal portions, the dis- 
cordance is well de\eloped, with marked angularit\' 
and truncation of lieds north of the Panoche Hills, 
and on the Stockton Arch pre-Miocene rocks are trun- 
cated across the whole width of the valley. 

Miocene Rocks 

Tiie .Miocene rocks of the Great \'allc\ ha\'e ver\' 
complex facies variations, and the stratigraphic nomen- 
clature, both formal and informal, reflects the man\ 



lithologic dissimilarities of the different depositional 
environments. In general, the basin contains nonmarine 
clavs, sands, and conglomerates along its margins, ma- 
rine near-shore sandstones in the intermediate areas, 
and marine, deep-water, shales and sandstones in the 
center. 

The seas w ere confined to the southern San Joaquin 
Basin during the early .Miocene but gradualh', prob- 
abl\- with some recessions, spread northward so that 
!)>■ late Miocene time marine sediments were being 
deposited along most of the western side of the Great 
\'alle\- at least as far north as \'acaville. 

The Miocene rocks were derived from the granitic 
iiigiilands on the east and south and from the Fran- 
ciscan terranes exposed on the west along the rising 
Diablo uplift between Coalinga and .Mount Diablo. 
.\long the southwest margin of the basin, granitic 
source areas also appear at times to have been pres- 
ent, perhaps as a result of uplifts in the area west 
of the San Andreas fault. 

Loii-er Miocene Rocks. Marine sediments of earl\- 
Miocene age are restricted to the southern San Joa- 
quin \'alley where they have been segregated into 
numerous units. On the west side of the basin these 
units have been named, in ascending order. Salt Creek 
Shale, Phacoides Sand, Lower Santos Shale, Agua 
Sand, Upper Santos Shale, Carncros Sand, and Media 
Shale. The east side equivalents are the \'edder Forma- 
tion, Pyramid Hill Sand, Jewett Silt, Freeman Silt, 
and the low cr portion of the Olccse Sand. In the Coa- 
linga-Kettleman Hills area the lower .Miocene marine 
rocks have been subdivided more loosel\' into the 
"N'aqueros" and lower "Temblor." 

Nonmarine lower Miocene rocks are represented 
along the south and southeast margin of the San Joa- 
quin basin by the upper part of the Tecu\a and 
Walker Formations, and north of Coalinga continental 
deposits that have been named the Zilch F<»rmation, 
or simpK" "continental Miocene," probabl\- include 
some lower Miocene rocks. In the soutiicrn Sacra- 
mento \'allcy such units as the \'allc\- Springs Forma- 
tion and the Kirker Tuff ma\' include deposits of early 
Miocene age. 

Uplift of the Ichachapi-San Emigdio area in early 
Aliocenc was accompanied by volcanism that laid 
down basalt and dacitc flows at the south end of the 
vallcw .A-sh beds and bentonites in the Freeman Silt 
and at the top of the \'edder also reflect volcanism in 
the lower Miocene. 

Unless one calls upon large lateral displacement 
along the San .Andreas fault, it is difficult to deter- 
mine through w hat inlet the seas entered the San Joa- 
quin Basin during lower Miocene time. No marine 
lower Miocene rocks occur an\w here immediately 
west of the San .Andreas fault opposite the San Joa- 
quin marine basin. This relationship of a thick marine 
section of rocks east of the San .Andreas fault adjacent 
to a nonmarine section west of the fault continues to 



1966 



Hackfl: Grkat V'ai.i.ky 



231 




Figure 7. Distribution and thickness of middle Miocene sediments in the Great Valley at the beginning of late Mio 
time. After Repenning (1960, fig. 9). 



Cil-<)I.(K;V Ol- NOKIHIKX C.M.IKOKMA 



Bull. 190 







EXPLANATION 




MARINE 
DEPOSITS 


CONTINENTAL 
DEPOSITS 


HeAvr LINE SHOWS PKCSEMT LIMIT* OF 
SEDIMENTARY NOCKS IN THE CENTRAL VALLEY 


SCALE IN MILES 


C 


10 30 


lO 










1 




Figure 8. Oislribution ond thickness of upper M 
After Repenning (1960, fig. 10). 



diments in the Greot Valley at the beginning of Pliocene tip 



1966 



Hackf.l: Griat Valli-y 



233 



show up on paleogeographic maps drawn to represent 
various intervals throughout the remainder of the iMi- 
ocene. 

The thickest sequence of lower Miocene rocks in 
the Great \'alle\' lies in the southwest portion of the 
basin where several thousand feet of marine sediments 
were deposited. Pulsating movements of the sea in the 
area of the San Joaquin Basin during lower Miocene 
time are suggested by basal conglomerates (or "grits") 
at the base of the Salt Creek Shale (base of iMioccne), 
at the base of the Phacoides Sand, and at the base of 
several units of the Vedder Sand. 

Middle Miocene Rocks. Deposition of marine rocks 
in the Great Valley in the middle Miocene, as in lower 
Miocene time, was limited to the southern half of the 
San Joaquin Basin. On the west side of the V'alley, 
these rocks have been assigned in ascending order to 
the Button Bed Sand, Gould Shale, and Devilwater 
Silt. On the east side, equivalent marine rocks are en- 
compassed in the Olcese Sand and Round Mountain 
Silt. In the Coalinga-Kettleman Hills area the middle 
Aliocene is represented by the upper part of the Tem- 
blor Formation. To subdivide the marine middle Mi- 
ocene rocks into more discreet and local units, espe- 
cially in the subsurface, many informal names are 
commonly used by petroleum geologists. In this cate- 
gory fall such names as Kettleman sand, Belridge 
sand, Nozu sand, Reserve sand. Upper and Lower 
Variegated, Big Blue, and lower Maricopa shale. 

A long, narrow trough which was the site of deposi- 
tion of the marine Temblor Formation occupied the 
area of the present Vallecitos syncline northwest of 
Coalinga (Fl\'nn, 1963). This trough may have pro- 
vided the outlet from the San Joaquin Basin to the 
western sea. 

Nonmarine sediments of considerable thickness were 
also deposited in the Great Valley during middle Mio- 
cene time. Areas of extensive nonmarine deposition 
occur throughout the basin north of Coalinga and 
along its eastern and southeastern margins. These cen- 
tral valle\- terrestrial beds have been called the Zilch 
Formation or "continental Miocene". At the southern 
extremity of the valley terrestrial deposits of middle 
Miocene age have been assigned to the upper portion 
of the Tecuya Formation, and north of the White 
Wolf fault and south of the Kern River similar rocks 
comprise the Bena Gravels. 

Middle Miocene was a time of local uplifts along 
the margins of the San Joaquin Basin. Evidence for 
this is found in the coarse Franciscan detritus found 
in the Big Blue and Upper and Lower X'ariegated 
Members of the Temblor Formation in the Coalinga 
area, and in the presence of nonmarine or very coarse 
deposits in the middle Olcese Sand and Round Moun- 
tain Siltstone (Bena fanglomerate lenses). 

As the middle Miocene seas were restricted to the 
southern end of the Great Valley only nonmarine de- 
posits, assigned to the Valley Springs Formation, are 



present in the Sacramento \'alle\-. West of Mount 
Diablo there are marine sands and shales of the Mon- 
terev group but they are not Great Valley deposits. 

The thickness of middle Miocene rocks varies to a 
great degree, depending on their position in the basin. 
The greatest accumulation appears to be in the north- 
ern Temblor Range, where the marine sediments arc 
more than 4,000 feet thick (Seiden, 1964). 

Upper Miocene Rocks. Deposition of marine rocks 
was more widespread during late Miocene time than 
earlier in the .Miocene, though the distribution and 
pcrsistcnc\- of the sea still favored the southern San 
Joaquin \'alle\', where more than 6,000 feet of strata 
were deposited. 

On the west side of the basin, the marine units of 
the upper Miocene are primaril\' shale and have been 
called the Reef Ridge, McLure, and Antelope Shales.' 
Locally on the west side very contrasting facies of 
shale, diatomite, chert, and even conglomerate were 
deposited adjacent to, and interspersed with, each 
other. Toward the east a great portion of the marine 
upper Miocene is taken up by a subsurface wedge of 
sand, which has been termed the Stevens Sand. Sands 
are also present in local channels in the subsurface 
near the west side of the basin, and have received such 
local names as Leuthholtz, "55.'>", and .\sphalto Sands. 
A similar environment appears to be present along the 
eastern limit of the Stevens Sand deposition, which 
was perhaps at the hinge line of the basin, where sands 
at the Rosedale and Bellevue oil fields have long, nar- 
row trends. East of the deep-water Stevens Sand prov- 
ince, marine rocks are represented by the widespread 
Santa Margarita sand of shallow marine origin. Other 
local marine upper Miocene units in the subsurface on 
the east side of the San Joaquin Basin have been named 
Fruitvale Shale and Wicker Sand. 

Towards the eastern margin of the San Joaquin 
Basin, the Santa Margarita sand grades into the_ upper 
portion of the nonmarine Bena Gravels. Xorthward it 
appears to interfinger with the nonmarine Zilch For- 
mation. Farther north, on the west side of the San 
Joaquin X'alley and in the southwestern Sacramento 
\'alle\-, the marine San Pablo Group appears to be the 
equivalent of the Santa Margarita. Whether or not 
continuous upper Miocene marine sediments e.xist in 
the subsurface from Mount Diablo to Fresno is not 
\et determined. 

Nonmarine rocks of probable late Miocene age are 
extensive on the east side of thejiorthcrD_5an_Ji3aquin 
X'alley and in the Sacramento X'alley as far north as 
Marvsville. In this area they have been assigned to the 
Mehrten and Zilch Formations, but commonl\- they 
are simpl\- referred to as "continental Miocene" by 
petroleum geologists. Other thick nonmarine deposits 
of coarse detritus are exposed in the Caliente Creek 
drainage of the southeastern San Joaquin \'alley and 
have been described and named the Bena Gravels. 

A substantial part of the eastern and southern San 
Joaquin \'alle\' received an accumulation of nonma- 



234 



Gioi.(x:y ok Northkrn Camkorma 



Hull. 190 



rinc cla\- and saml Jiiring tiic late Miocene; these rocks 
comprise the lower part of the Chanac Formation. 
This formation is one manifestation of the orogen\- 
that elevated the cast side of the San Joaquin \'alle\ 
near the end of Miocene time. Bv means of the uplifts 
that came into heing during this time, the present gen- 
eral structural configuration of the Great X'alley Basin 
was formed. 

Pliocene Rocks 

' The tectonic movements w hich began in the upper 
Miocene continued into the Pliocene and resulted in 
considerahic erosion, particularl\- along the edges of 
the San Joaquin Valley. As a result. Pliocene deposits 
of continental origin are found in all parts of the \'al- 
Icy. Regional uplifting in most of the \'alle\' continued 
throughout Pliocene time^and niarine waters were able 
to invade only the southern and western portions of 
the San Joacjuin Basin. 

Marine rocks of the lower and middle Pliocene have 
been assigned to the Etchegoin Formation, although 
in the vicinity of Coalinga the lower portion of the 
undifferentiated Etciiegoin is called the Jacalitos For- 
mation. The most extensive marine member of the 
Etchegoin is the Macoma Claystone, a subsurface unit. 
The Macoma Cla\stone extends well east of the main 
mass of the Etchegoin, and it separates the nonmarine 
Chanac Formation from the overlying terrestrial Kern 
River Formation (Am. Assoc. Pet. Geologists, 1957, 
No. 8). 

The upper portion of the marine Pliocene strata has 
been named the San Joaquin Formation, which is best 
developed in the deepest portion of the San Joaquin 
emba\-ment. The San Joaquin Formation represents 
the last stand of marine waters in the Great Vallev. 

.Marine [^lioccnc rocks attain a gross thickness of 
somewhat over 5,000 feet and are composed of cla\- 
stone, sandstone, and conglomerates. 

The extensive continental deposits of the Pliocene 
on the east side of the San Joaquin \'alley have been 
assigned to the Chanac and Kern River Formations 
and those in the western San Joaquin Valley arc called 
the Tulare Formation. In the northern San Joaquin 
V^allev the Pliocene rocks include parts of the Mehr- 
ten and Laguna F'ormations. Fartiier nort h, in the Sac^ 
ramento Valle_\-, the nonmarine Pliocene rocks have 
been assigned to the Tehama Formation. In the west- 
ern part of the Sacramento Valley, north of .Mount 
Diablo, continental beds equivalent to the Laguna For- 
mation have been called the Wolfskill Formation. The 
Wolfskin overlies a lower Pliocene tuff called the 
Pinole or Eawlor Tuff. Further north, a similar tuff 
called the Xonilaki Tuff occurs near the base of the 
Tehama Formation. 

The nonmarine Pliocene rocks vary considerably in 
lithology, depending on the local source area. As an 
example, beds equivalent to the Tehama have been 
called the Tuscan Formation where they are largely 
derived from a volcanic terrain. In general the lith- 



ology of these continental deposits consist of clay- 
stones, sandstones, and conglomerates, with the coarser 
units becoming more common as source areas are ap- 
proached. The greatest thickness of nomiurine Plio- 
cene occurs in the Tehama where a thickness of about 
2,000 feet is present. 

Pleistocene and Recent Rocks 

Rocks of Pleistocene and Recent age occur through- 
out the Great N'alley. They are all continental in origin 
and generall\- grade downward into similar Pliocene 
units. The\- are discussed in greater detail in this bul- 
letin in the following article b_\- J. V. Poland and R. E. 
Evenson. 

.\t the northern extremity of the valley a coarse 
fluvial unit of predominant red color, called the Red 
Bluff Formation, attains a thickness of about 100 feet. 
In the southern part of the valle\- the nonmarine Pleis- 
tocene sediments have been assigned to either the 
Tulare Formation on the west side or to the Kern 
River Formation on the east. Both the Tulare and 
Kern River Formations have lithologies indicating local 
sources. It is common for the Tulare to be composed 
of shale-pebble conglomerates derived from the up- 
lifted Temblor Range, and the equivalent Kern River 
Formation is generally formed of granitic sands and 
conglomerates derived from erosion of the Sierra Ne- 
vada. The Tulare and Kern River Formations attain 
thicknesses of several thousand feet, with the maximum 
being about 5,000 feet on the downthrown side of 
the White Wolf fault south of the Bakcrsfield Arch. 

Recent alluvium and lake deposits cover most of the 
central lower parts of the present Great \'^allc\-. 



IGNEOUS ACTIVITY 

The areas of igneous activity in the Great X'alley of 
California are, curiously enough, at its two extremities. 
In the northern Sacramento \^alle\', volcanic rocks 
are present at the surface and in the subsurface from 
south of the .Marxsville Byttcs north to the latitude of 
Chico. At the south end of the San Joaquin \'alle\, vol- 
canic flows are found in surface and subsurface of 
the Tejon emba>-ment, and in the outcrop north of 
the White W'olf fault in the vicinit\- of Bena. 

The Marys\ ille Buttes, which form an isolated top- 
ographic prominence about 2,000 feet high northeast 
of the town of Marysville, are the most prominent 
igneous feature in the Great \'alley. The Buttes are 
circular in shape, about 10 miles in diameter, and their 
topography reflects their geology. The\- consist of 
a central core of andesitc porph\r\- and tuff sur- 
rounded by a ring of sediments, and these sediments 
are embraced in turn by a ring of andesite tuff and 
breccia which extends to the Valley alluvium. Intru- 
sions of rhyolite porphyry are scattered through the 
sediments and in the central core. The porphyries 
were the first volcanic rocks emplaced and appear to 
have been injected at a slow rate; the final igneous 
activity, however, was an explosive phase fonuing a 



1966 



Hackk.l: Gri at V'allkv 



235 




STOCKTON 

^"^ MT DIABLO - >P 



EXPLANATION 



MARINE 
DEPOSITS 



CONTINENTAL 
DEPOSITS 



HEAVY LIN 
SEDIMENTARY 



: SHOWS PRESENT LIMITS 
ROCKS IN THE CENTRAL 



SCALE IN MILES 



SOURCES 

NORTH OF FRESNO-- 
Many sources 

SOUTH OF FRESNO — 

Hoots, Beor.and Kleinpell, l954o, 
with some modification. 




AS 



122* 

_J 



Figure 9. Distribution and thickness of Pliocene secJiments in the Great Volley ot the beginning of Pleistocen 
After Repenning (1960, fig. 11). 



236 



Gl-.OUXiY OF NORTHKRN CaI.IIOKMA 



Bull. 190 



volcano one mile in diameter which ejected fragments 
of andesitc varying in size from boulders to fine- 
grained tuff. Sul)surfacc information shows that the 
volcanic rocks have been intruded into Upper Cre- 
taceous and Eocene sediments as u ell as into the lower 
part of the Tehama Formation, thus fixing the time of 
the intrusion. 

• North of the Marvsvillc Buttes, volcanic flows of 
basalt are common, and the\- gcncrall\- occur near or at 
the base of the Tehama Formation. 

The volcanic rocks at the south end of the San 
Joaquin \'alle\' consist of basalt and dacite flows. 
These rocks are enclosed within lower Miocene sedi- 
ments and most appear to have been submarine flows. 

STRUCTURE 

f Structurally', the Great X'alley of California is a 
large, elongate, northwest trending, asymmetric trough. 
This trough has a long stable eastern shelf, which is 
supported by the buried west-dipping Sicrran slope, 
and it has a short western flank, which is formed by 
the steep upturned edges of the basin sediments. 

Four major periods of tcctonism are recorded in 
the sedimentary section of the Great \'alley. These are 
the post-Moreno, the pre-Domengine, the pre-Pliocene, 
and the mid-Pleistocene. These periods of ma.ximum 
structural activity are responsible for the major 
changes in the configuration of the basin throughout 
geologic time. The most severe period of deformation 
was in the mid-Pleistocene, and it brought to a climax 
die structural evolution of the basin. 

The Great \'alle\' geos\nclinc with its pronounced 
regional southward tilt is significantiv interrupted by 
two cross-valley faults. These major Structures, the 
Stockton fault and the White Wolf fault, are associ- 
ated with the cro.ss-valle\' structural highs known as 
the Stockton Arch and the Bakersfield Arch. 

The Stockton .Arch, located in the central portion 
of the basin, extends from the Sierran slope across to 
the Diablo uplift of the western flank. The high ap- 
pears to have been formed by Eocene time, though 
uplift mav have continued into the Miocene. Most of 
the present- elevation of the arch appears to be due 
to upward movements on the south side of the Stock- 
ton fault, though stratigraphic evidence suggests that, 
when the arch first began, its axis lay further south 
in the \icinit\- of Modesto. 

The Bakersfield Arch, in the southern end of the 
basin, also extends from the Sierran slope westward, 
but appears to terminate near the axis of the gcosyn- 
cline instead of continuing on to the western flank. 
This arch apparcntl\- formed the southern edge of the 
vallev dcpositional basin until middle Eocene time. The 
barrier was then overwhelmed and the Eocene seas 
spilled into the sub-basin that is sometimes called the 
Tejon embayment south of the White Wolf fault. 

The Tejon cml)a\'ment south of the Bakersfield 
Arch, and in particular south of the White Wolf fault, 
has been a stimewhat distinct structural unit through 



geologic time and has been thought by some geologists 
to be more closely related to a group of intermontane 
basins formed during the lower TertiarN- to the west 
in the adjacent Coast Ranges. Evidence for this is 
found in the similarit\' of sections in the Oligocene 
and Miocene, for example, in the red bed sequences 
in the "Eecuya Formation of the valley and the Scspc 
Formation of the Coast Ranges. The Coast Range bas- 
ins, west of the San .Xndrcas fault, are thought to have 
been offset northward along the fault so far that thcs' 
are no longer adjacent to the vallev basin. .More de- 
tailed structural and stratigraphic studies arc needed, 
however, before such a h\p<)thcsis can be regarded 
as proven. 

Other subsidiary basins along the Great \'allcy 
trough also complicate the concept of a simple south- 
erly tilted basin. In the Sacramento part of the trough, 
for example, such basins are in the vicinit\- of Colusa 
and between Rio \'ista and the Kirby Hills. 

The mid-Pleistocene orogen\' formed man\' flex- 
ures throughout the Great \'alle\-, and it also reju- 
venated many of the folds that had formed during 
previous orogenic periods. Much of the disturbance 
took place along the short mobile western flank, where 
numerous folds and faults are now particularly evi- 
dent. Man\' of these flexures are as\nimetric and asso- 
ciated with comprcssional faults of the rexerse tvpe. 
The magnitude of the folds decreased eastward but 
was still strong enough to cause the formation of lines 
of folding out to, and even beyond, the basin axis. 
The eastern shelf is relatively free of folds, and faulting 
in this region is of the normal tensional type. 

The western mobile flank flexures are too numerous 
to enumerate, but becau.se of their economic impor- 
tance those of the Central X'alley will be summarized. 
Many of these folds are evident at the surface, but 
because of the extensive alluvium cover, many other 
flexures are known onh" from seismic data and well 
bore information. In the Sacramento \'allev significant 
anticlinal trends are found at Corning, Willow,s-Bee- 
hive Bend, Sites, Rumsey Hills, Wilbur Springs, Dun- 
nigan Hills, Lodi-Thornton, Rio \'ista, and .McDonald- 
Roberts Island. In the San Joaquin \'allc\-, most of 
the large anticlines arc in the southern portion; among 
these arc the Coalinga Xose-Kettlenian Hills-Lost Hills 
Trend, North and South Belridge, Salt Creek-C\ niric- 
McKittrick Front Trend, Elk Hills, Buena X'ista Hills, 
Wheeler Ridge, Coles Levee, Ten Sections, and Grce- 
le\-Rio Bravo. 

Faults are numerous in the Great \'allc>-. In the 
Sacramento \'alle\' the most prominent faults are those 
( i ) as.sociatcd w ith the Willows-Beehive Bend trend, 
(2) reverse faults at the north flank of Dunnigan 
Hills, (3) faults north of Mount Diablo near Willow 
Pas.s, and (4) the .Midland fault which traverses the 
Rio Vista gas field. This latter fault was active during 
Eocene time as demonstrated b_\- the different thickness 
of equivalent rock units on each side of it. In the San 



1966 



Hac.kki.: Grkai V'ai.i.ky 



237 




Photo 1. Natural gos well being drilled at Morysville Buttes. Photo by Edmund W. Kiessling. 



Joaquin \'alley, faults with considerable displacement 
are common. The Stockton and White Wolf faults 
have already been mentioned. In the reverse or thrust 
category are such faults as (1) the McKittrick thrust 
in western Kern County, (2) the Pleito thrust in the 
Tejon embayment, and (3) the Edison fault in the 
outcrop southeast of Bakersfield. Large normal faults 
which bear mentioning are the Kern Gorge fault and 
its associated echelon members the Round Mountain 
and Mount Poso faults; also deserving mention are 
the group of faults in the Edison and Mountain View 
oil fields, some of which appear to cut only middle 
Miocene and older sediments while others are present 
only in the Pliocene and upper Miocene. 

Tectonic activity, though reaching its clima.x in the 
mid-Pleistocene, is still continuing in the Great \'alle\- 
as borne out by seismic disturbances, the most recent 
of which was the destructive earthquake of 1952 that 
originated along the White Wolf fault. 

ECONOMIC GEOLOGY 

The mineral economic resources of the Great \'alle\- 
are summarized in this bulletin in an article prepared 
by Earl W. Hart and will be onl>- commented upon 
here. Briefly the highlands on each side of the basin 
have \ielded millions of dollars from the metallic min- 



erals recovered; prime examples, of course, are the 
gold of the Sierra Nevada and the mercury associated 
with the Franciscan in the Coast Ranges. In the Great 
\'alley itself, although these minerals are also found, 
the mineral commodities of greatest value are oil and 
gas, water, and gravel deposits. 

The sedimentary section of the Great Valley has 
been found to be an enormous storehouse for oil and 
gas. The Sacramento \"alley has been found lacking 
in anv important oil resources, but gas in economic 
quantities has been produced from at least 25 fields. 
Much of this gas has been reservoired in rocks of 
Eocene and Late Cretaceous age. In the San Joaquin 
\'alle\ , both oil and gas arc prevalent, though the oil 
resources are concentrated in the central and southern 
part. Oil has been found, in significant amounts, as far 
north as the latitude of Fresno; north of there the hy- 
drocarbon accumulations are gas. The billions of bar- 
rels of oil found in the San Joaquin \'alley have been 
reservoired in sediments ranging in age from Late 
Cretaceous to Pleistocene; however, the majorit)- have 
been produced from Miocene and Pliocene rocks. Of 
the dry gas produced in the San Joaquin Valley most 
in the southern end comes from Pliocene rocks and in 
the northern portion most is from Upper Cretaceous 
rocks. Several theories have been advanced to explain 



238 



GlOLCXiY OK NORTIIIRN CaI.IKORMA 



Bull. 190 



why oil is foimd chiefly in the San Joaquin Valle\' 
and dry gas occurs largelv in the Sacramento Valley. 
It is likel\- that the distribution is related to the source 
material in the sediments; certainl\-, the organic con- 
tent of the F.ocene and Cretaceous shales of the Sacra- 
mento is very different from the Miocene and Pliocene 
shales of the San Joaquin. 

The water resources of the Great X'^allcy are be- 
coming more and more important as the population in- 
creases at an accelerated rate. The available waters of 
the \alle\' come from two main sources: ( 1 ) the num- 
erous streams flowing westward from the Sierra Ne- 
vada, and (2) the ground-water reservoirs. Most of the 



ground-water resources e.xist in the xounger portion 
of the sedimentary column — the Pliocene, Pleistocene, 
and Recent alluvium. The following article in this 
bulletin by Poland and F.venson presents a more thor- 
ough treatment of this subject. 

Again, chiefly as a result of the increase in popula- 
tion, the sand and gravel deposits suitable for road 
building and construction arc becoming more and 
more important. The broad expanses of stream gravels 
along the major streams flowing from both sides of the 
vallcv offer an aimf)st unlimited source. Their eco- 
nomic utilization usually- is dependent onl\ on the 
distance to the market. 



REFERENCES 



Almgren, A 


A., and Schlax, W. 


N., Jr., 1957, Post-Eocene 


age of 


"Markley 


Gorge" fill, Socrome 


nto Valley, California: Am 


Assoc. 


Petroleum 


Geologists Bull., v. 41 


no. 2, p. 326-330. 




American A 


sociotion of Petroleum 


Geologists, 1951-1960, Co 


relation 



* (Son Jooquin Valley and Socramento Volley] Coli- 
Assoc. Petroleum Geologists, Pocific Sec, nos. 1, 6, 8, 



sectio 
fornio 
9, 10, 11, and 13. 

Bailey, E. H., ond Irwin, W. 
and Cretaceous graywackes 
ramento Valley, Californio 
V. 43, no. 12, p. 2797-2809 

Boiley, E. H., Irwin, V^. P., ond Jones, D. L., 1964, Franciscan and 
reloted rocks and their significance in the geology of western Cali- 
fornio: California Div. Mines and Geology Bull. 183, 177 p. 

Callawoy, D. C, 1964, Distribution of uppermost Cretaceous sands in 



P., 1959, K-feldspor content of Jurossic 
of the northern Coast Ranges ond Sac- 
Am. Assoc. Petroleum Geologists Bull., 



the 



rthe 



of Californi( 



San 



5-18. 



□ tigraphy of the Sacramento 
Soc, Selected Papers, v. 1, 



amento-i 
Joaquin Geol. Soc, Selected Papers, v. 

Chuber, Stewart, 1962, Late Mesozoic str 
Valley [California]: Son Joaquin Geol. 
p. 3-16. 

Cross, R. K., 1962, Geology of the Corrizo-Cuyama basin, in Guide- 
book, Geology of Carrizo Ploins and San Andreas foult: San Joaquin 
Geol. Soc. and Am. Assoc. Petroleum Geologists-Soc Econ. Paleon- 
tologists and Mineralogists, Pacific Sec. ] field trip], 1962, p. 27-35. 
■ Dibblee, T. W., Jr., 1961a, Geologic structure of the San Emigdio 
Mountains, Kern County, California: Soc Econ. Paleontologists and 
Minerologists-Soc Econ. Geologists-Am. Assoc. Petroleum Geologists, 
Pacific Sec, and San Joaquin Geol. Soc, Guidebook, Spring field 
trip, 1961, p. 2-5. 

1961b, Geologic map, San Emigdio Mountains [California]: Soc. 

Econ. Paleontologists and Minerologists-Soc. Econ. Geologists-Am. 
Assoc. Petroleum Geologists, Pacific Sec, and Son Joaquin Geol. 
Soc, Guidebook, Spring field trip, 1961, in pocket. 

1962a, Displacements on the Son Andreas rift zone and related 

structures in Carrizo Plain and vicinity [California!, in Guidebook, 
Geology of Carrizo Plains and Son Andreas fault: San Joaquin Geol. 
Soc and Am. Assoc. Petroleum Geologists-Soc Econ. Paleontologists 
and Mineralogists, Pacific Sec. [field trip], 1962, p. 5-12. 

1962b, Geologic map of Caliente and Temblor Ranges, Son Luis 

Obispo ond Kern Counties, Californio, in Guidebook, Geology of 
Carrizo Plains and San Andreas fault: Son Joaquin Geol. Soc. and 
Am. Assoc. Petroleum Geologists-Soc Econ. Paleontologists ond Min- 
eralogists, Pacific Sec. [field tripj, 1962, in pocket. 
■Dibblee, T. W., Jr., Bruer, V^. G., Hackel, O., and Warne, W. H., 
1965, Geologic mop of the southeostern Son Joaquin Valley-Kern 
River to Grapevine Canyon, in Geology of southeastern Son Joaquin 
Valley, California: Am. Assoc Petroleum Geologists-Soc Econ. Geol- 
ogists-Soc Econ. Paleontologists ond Mineralogists, Pacific Sec, 
Guidebook, p. 7. 

Durham, J. W., 1962, The late Mesozoic of cenlrol California: Colifor- 
nia Div. Mines ond Geology Bull. 181, p. 31-38. 

Flynn, D. B., 1963, The San Benito Wollhom Canyon trough-possible 
oil province?, in Guidebook to the geology of Salinas Valley and 
the San Andreas fault: Am. Assoc. Petroleum Geologists-Soc. Econ. 
Paleontologists and Mineralogists, Pocific Sec, Ann. Spring field trip, 
1963, p. 27-33. 

Goudkoff, P. P., 1945, Stratigraphic relations of Upper Cretaceous in 
Great Volley, Californio: Am. Assoc. Petroleum Geologists Bull., v. 
29, no. 7, p. 956-1007. 



side of the Sacramento 
nd Geology Bull. 181, 



California: 



Gribi, E. A., Jr., 1963, The Solinos basin oil province, in Guidebook 
to the geology of Salinas Valley ond the Son Andreas foult: Am. 
Assoc Petroleum Geologists-Soc Econ. Paleontologists ond Mineral- 
ogists, Pacific Sec, Ann. Spring field trip, 1963, p. 16-27. 

Hoffman, R. D., 1964, Geology of the northern San Jooquin Valley 
[Californio]: Son Jooquin Geol. Soc, Selected Papers, v. 2, p. 30-45. 

Hoots, H. W., Bear, T. L., and Kleinpell, W. D., 1954, Geologic sum- 
mary of the Son Joaquin Valley, California, [pt.] 8 in Chop. 2 of 
Johns, R. H., ed.. Geology of southern California: California Div. 
Mines Bull. 170, p. 113-129. 

Huey, A. S., 1948, Geology of the Teslo quadrangle, California: Cali- 
fornia Div, Mines Bull. 140, 75 p. 

Irwin, W. P., 1957, Fronciscon group in Coast Ranges ond its equiv- 
olents in Socromento Valley, California: Am. Assoc Petroleum Geol- 
ogists Bull., V. 4, no. 10, p. 2284-2297. 

Kirby, J. M., 1943, Upper Cretaceous stratigraphy of the west side of 
Socromento Volley south of Willows, Glenn County, California: Am. 
r Assoc Petroleum Geologists Bull., v. 27, no. 3, p. 270-305. 

Lachenbruch, M. C, 1962, Geology of the 
Valley, California: Colifornio Div. Mil 
p. 53-66. 

Loiming, Boris, 1943, Eocene forominiferol correlations 
Colifornio Div. Mines Bull. 118, p. 193-198. 

Murphy, M. A., ond Roddo, P. V., 1960, Mollusca of the Cretaceous 
Bold Hills Formation of California: Jour. Paleontology, v. 34, no. 5, 
p. 835-858. 

Owens, L. D., 1963, Regional geology of the central portion of the 
Great Valley of California, in Central portion of Great Valley of 
Californio, Son Juon Boutisto to Yosemite Valley: Geol. Soc Sacra- 
mento Guidebook, Ann. field trip, 1963, p. 88-97. 
■■Payne, M. B., 1962, Type Ponoche group (Upper Cretoceous) ond over- 
lying Moreno and Tertiary strata on the west side of the Son Jooquin 
Valley: Californio Div. Mines ond Geology Bull. 181, p. 165-175. 

Repenning, C. A., 1960, Geologic summary of the Centrol Valley of 
California with reference to disposal of liquid radioactive waste: 
U.S. Geol. Survey TEI Rept. 769, 69 p. 
"Rudel, C. H., 1965, Rock units of the general east side area Cottonwood 
Creek to Tejon Hills, in Geology of southeostern San Joaquin Valley, 
California: Am. Assoc. Petroleum Geologists-Soc. Econ. Geologists-Soc. 
Econ. Paleontologists ond Minerologisis, Pacific Sec, Guidebook, p. 7. 

Sofonov, Anotole, 1962, The challenge of the Sacramento Valley, Coli- 
fornio: California Div. Mines and Geology Bull. 181, p. 77-100. 

Seiden, Hy, 1964, Kettlemon Hills oreo [Colifornio]: Son Joaquin Geol. 
Soc, Selected Papers, v. 2, p. 46-53. 

Silcox, J. H., 1962, West Thornton and Walnut Grove gas fields, Cali- 
fornia: California Div. Mines and Geology Bull. 181, p. 140-148. 

Teitsworth, R. A., 1964, Geology ond development of the Lothrop gas 
field. Son Joaquin County, California: Son Joaquin Geol. Soc, 
Selected Popers, v. 2, p. 19-29. 

Wolrond, Henry, ond Gribi, E. A., Jr., 1963, Geologic mop of part of 
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geology of Salinas Valley ond the Son Andreas fault: Am. Assoc. 
Petroleum Geologists-Soc. Econ. Paleontologists ond Mineralogists, 
Pocific Sec, Ann. Spring field trip, 1963, in pocket. 
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Son Joaquin Valley, California: Am. Assoc. Petroleum Geologists-Soc 
Econ. Geologists-Soc. Econ. Paleontologists and Mineralogists, Pocific 
Sec, Guidebook, p. 8-9. 

While, C. A., 1885, On the Mesozoic ond Cenozoic poleonfology of 
California: U.S. Geol. Survey Bull. 15, 33 p. 



HYDROGEOLOGY AND LAND SUBSIDENCE, 
GREAT CENTRAL VALLEY, CALIFORNIA * 

Bv J. F. Poland and R. E. Evenson 
U.S. Geological Survey, Sacramento, California 



The first part of this paper describes the significant 
geomorpliic features, presents a tentative correlation 
of the geologic units that constitute significant ele- 
ments of the tremendous ground-water reservoir in 
the Great Central Valley, summarizes the post-Miocene 
geologic history, and describes briefly the ground- 
water conditions of the valley. It is a supplement to 
the more comprehensive companion paper by Otto 
Hackel on the geology of the valley from Late Ju- 
rassic time to the end of Pliocene marine deposition. 

The second part of the paper describes the extent 
and magnitude of the land subsidence that is taking 
place in the San Joaquin Valley, caused chiefly b\- 
intensive pumping of ground water and the resulting 
decline in artesian head. Subsidence of the land sur- 
face is a critical aspect of the hydrogeology because 
it poses serious problems in construction and mainte- 
nance of engineering structures for water transport, 
especially large canals or aqueducts. 

The first part of this paper is based largely on U.S. 
Geological Survey studies in the Sacramento Valley 
by Olmsted and Davis (1961), and in the San Joaquin 
Valley by Davis and others (1959 and 1964). The 
authors are also indebted to representatives of the 
Pacific Gas and Electric Company and the Sacramento 
Municipal Utility District for providing background 
data that facilitated estimates of ground-water \\ ith- 
drawal for irrigation use in 1964. 

HYDROGEOLOGY 
Geomorphology 

The Central Valley constitutes a structural down- 
\Varp extending more than 400 miles from Redding on 
the north to the Tehachapi Mountains on the south; 
it has an average width of about 40 miles, and spans 
15,000 sq. mi. or about one-tenth of the State. About 
the northern third of the valley is known as the Sac- 
ramento Valley and the southern two-thirds as the 
San Joaquin Valley. Drainage from the Sacramento 
Valley is southward through the Sacramento River 
to its confluence with the San Joaquin River, near 
Suisun Bay, and then westward through San Francisco 
Bay to the Pacific Ocean. The northern part of the 
San Joaquin Valley drains northward through the San 
Joaquin River but the southern part of the valley is 
a basin of interior drainage tributary to ephemeral 

* Publication authorized by the Director, U. S. Geological Sur\'ey. 



lakes in the trough of the vallc\ . These often nearly 
dry lake areas arc known as Kern, Buena V'ista, and 
Tulare Lake Beds. 

The valley floor is divided, as shown on figure 1, 
into four geomorphic units: (1) dissected uplands, (2) 
low alluvial plains and fans, ( 3 ) river flood plains and 
channels, and (4) overflow lands and lake bottoms. 

Dissected uplands fringe the valle\- along its moun- 
tain borders and are underlain principally b>' uncon- 
solidated to semiconsolidated continental deposits of 
Pliocene and Pleistocene age which have been struc- 
turally deformed. Topographic expression of these 
uplands ranges from dissected hills with relief of sev- 
eral hundred feet to gently rolling lands where relief 
is only a few feet. 

Lo\\' alluvial plains and fans that border the dis- 
sected uplands along their valleyw ard margins are gen- 
erally flat to gentls' undulant and are underlain by 
undeformed to slightly deformed alluvial deposits of 
Pleistocene and Recent age. 

The river flood plains and channels lie along the 
Sacramento, San Joaquin, and Kings Rivers in the 
axial parts of the valley and along the major streams 
on the eastern side of the valley. Those rivers that 
are incised below the general land surface have well- 
defined flood plains; but in the axial trough of the 
valley, the rivers are flanked by low-l\ing overflow 
lands and there the flood-plain and channel deposits 
are confined to the stream channel and to the natural 
levees that slope away from the river. 

Overflow lands and lake bottoms include the historic 
beds of Kern, Buena Vista, and Tulare Lakes in the 
southern part of the valley, and also the lowlands 
adjacent to the natural levees of the major rivers. 
They are almost level and are underlain by lake and 
swamp deposits of PvCcent age. 

Geologic Units 

The deposits containing fresh ground water are 
principally unconsolidated continental deposits of Pli- 
ocene to Recent age that extend to depths ranging 
from less than a hundred to more than 3,500 feet. 
Locally, marine sediments contain fresh water and in 
other areas continental deposits contain saline water, 
but such conditions are of minor extent. Table 1 shows 
a tentative correlation of geologic units of hydrologic 
significance in the ground-water reservoir of the Cen- 
tral V^alley and table 2 is a resume of the post-Miocene 



240 



Ci.oi.tK;v OK Nt)Kriii.uN California 



Hull. 190 



EXPLANATION 

□ 

Overflow lands and 
lake b ot I oms 




20 20 40 60 80 Miles 



Figure 1. Geomorphic map of the Great Cenlrol Valley. Geomorphic units after Davis and others (1959, pi. 1) and Olmsted and Davis (1961, pi. I). 



1966 



Poland and Evknson: Great \'alley 



241 



CORRELATION CHART OF GEOLOGIC UNITS H YOR OLQG 1 CA LLY SIGNIFICANT IN THE CENTRAL VALLEY. CALIFORNIA 
(Estimaled range in thickness indicaled Kilhin paienlhesesi 


SACRAMENTO VALLEY 




SAN JOAQUIN VALLEY 






Mokelumne area 1 
(Piper and others, 
1939) 


Stanislaus area 
(Dav IS and Ha 1 1 . 1959) 


West and south s ides 
(Var lous authors i 


West side | NoMheast side | 


East side 


r 


1 

Rivec. 1 lood-bas in. 

>nd al luv la 1 -Ian 

depos 1 ts 

(0-150" It) 


River and al luvia 1 - 
fan depos i ts 
(0 150+ ft) 


River and f lood- 
bas in depos its 
(0-100 ft) 


River -channe 1 and 

f 1 ood -pla in depos i ts 

(0-25 ft) 


River -channe 1 and 

1 1 ood-p la in depos i ts 

(0 50 ft) 


Alluv la 1 • f an. f 1 ood- 
pla in and f lood- 
bas in depos i ts 
(0-150+ ft) 


<-> 

o 


Ktd tlufi 
Foraation 
(0-50* ft) 


Victor Format ion 

and re lated depos i ts 

(O-lOOi ft ) 

Fanjiomerate from 

the Cascade Range 

(0-5Q0+ ft ) 

1 


Victor Forniation 
(0-150+ ft) 

Laguna Format i on 
and related 


Victor Formation 

and re lated depos i ts 

(0-150 ft) 


Modesto Fm of Dav is and 
. Hal 1. 1959 (50-100 ft) 

Riverbank Format ion of 

Dav IS and Ha 1 1 . 1 959 

(150-200 ft) 


1 
X 

1 


ICotcoran Clay^ Memberl 
1 b. 0.6(+)<10' years | 


Turlock Lake Fm of 

Oavis and Ha 1 1 . 1959 

(350-850 ft) 


Tulare Formation 
(0-3.000 ft) 


u 


Tiliam 1 1 Tuscan Fofniat ion 


cont inenta 1 
depos 1 Is 
1 (0-1 . 000+ ft ) 

T 
1 

Mehr ten Format ion 

and related 

volcan ic r ochs • 

(0-400 fl ) 


1 Laguna Formation 
j (0-400 ft ) 

T 
1 

Mehr ten Format ion 
(75-400 ft 1 


Mehrten Formation 
(800-1 .200 ft ) 


San Joaguin Formation 
lO- 1.800 ft) 

Etcfiego in Formal ion 
(0-2.000 ft) 


Nonlslii Tuff Membei KO-I.OOOt It) 
s. 3.3»10' years I 


1 Fo-^ation 1 
1 (0-2. 50O* It ) 


T 

1 
1 


e 




1. E»ir nfltn and otfier s 


1 
1 

. 1 964 


1 


1 
X 

t), landa 


R J 1965, p. 131 



geologic history. Because of space limitations, the 
reader is referre(d to the cited references for infor- 
mation on the physical and water-bearing character 
of the individual geologic units listed in table 1. 

The unconsolidated continental deposits consist 
chiefly of alluvium but in some areas include wide- 
spread lacustrine and marsh or estuarine sediments. 
These deposits constitute late Cenozoic fill in the 
structural trough, whose axis in the San Joaquin Val- 
ley lies west of the present topographic axis of the 
valley. Appreciable folding and ininor faulting also 
has occurred; however, these structural features have 
had no significant barrier effect on ground-water 
movement. 

Consolidated rocks form the boundaries beneath and 
on the flanks of the productive ground-water reservoir 
in the unconsolidated deposits. Only minor quantities 
of water occur in joints or fractures in the consoli- 
dated rocks in the Sierra Nevada, and the principal 



water supply to the valley — the stream runoff — passes 
over them. 

Ground-Water Occurrence and Use 

Ground water occurs under both confined (arte- 
sian) and unconfined (water table) conditions in the 
Central \'alley. The degree of confinement varies 
N\ idely because of the heterogeneity of the continen- 
tal deposits. In the big alluvial fans on the east side 
of the San Joaquin \'alle\-, the ground water is uncon- 
fined. The most extensive confined aquifer is the ma- 
jor aquifer s\stem overlain by the Corcoran Clay 
Member of the Tulare Formation (table 1), which 
covers more than 5,000 square miles in the San Joaquin 
Valley. 

Recharge to the ground-water reservoir is b\ infil- 
tration of rainfall, infiltration from streams, canals, and 
ditches, b\- infiltration of excess irrigation \vater, and 
b\ underflow entering the valley from tributary 
stream can\ons. 



242 



Geology of Northfrn California 
table 2.-resume of post-miocene geologic history. 



Bull. 190 



Epoch 


Coast Ranges 


Central Valley 


Sierra Nevada 


Pliocene 


Folding and faulting on 
regional scale in late 
Pliocene time outlines 
present form of ranges. 

Northern part of central 
Coast Ranges under- 
going subacrial erosion, 
concurrently with de- 
position of marine sedi- 
ments in local basins in 
southern part of ranges 
during early and middle 
Pliocene time. 


Deposition of marine sediments in southwestern part of valley during 
early and middle Pliocene time. 

Streams from Sierra Nevada depositing generally fine-grained alluvium 
on east side, including much coarse-grained volcanic detritus in early 
Pliocene time. 

All the valley was above sea level in late Pliocene time. Great thick- 
nesses of continental deposits accumulating in downwarping basins 
along western and southern margins of valley. 

Extensive lake occupies western part of valley and present foothill area 
in late Pliocene time. 

Igneous activity pushed up an andesitic plug through Sacramento \'alley 
sediments shattering or deforming them and forming the Sutter 
Buttes. Later rhyolitic domes and necks intruded the plug and 
around its periphery. 


Relative structural sta- 
bility, only minor 
crustal movement. 

Great volcanic activity; 
consequent streams 
erode volcanic deposits 
and move them toward 
the Central Valley. 


Pleistocene 


Major faulting and fold- 
ing accentuates exist- 
ing structures. Erosion 
of mountains with de- 
position in intermon- 
tane valleys. 


Deposition of coarse alluvial deposits by streams draining Sierra Nevada 
contemporaneous with dissection of tilted older alluvial-fan deposits. 

Extensive lake in San Joaquin \'alley deposits diatomaceous clay. 

Lowering of sea level and climatic changes during Pleistocene glaciations 
cause major rivers and tributaries to excavate trenches graded to 
lower base level or to mountain valley downcutting. Alluvial fans on 
east side tilted with Sierra Nevada block. Coast Range streams con- 
tinue to build alluvial fans in downwarping area on west side of 
valley. Several lake clays of variable extent deposited in late Pleisto- 
cene time. 


Several stages of glacia- 
tion in higher parts of 
range. Glacial scouring 
locally important in 
modifying land forms. 

Last major uplift of 
range along faults on 
eastern margin with 
additional westward 
tilting. 


Recent 


Subaerial erosion forms 
present topography. 
Minor structural move- 
ments continuing to 
present; many faults 
and folds still active; 
earthquakes frequent. 


Deposition of stream-channel, alluvial-fan, overflow, and lacustrine 

deposits contemporaneous with mild dissection of tilted alluvial fans 

on east side of valley. 
Deposition of broad coalescing alluvial fans on west side and south end 

of valley. Sediments generally finer grained than Pleistocene deposits. 
Trenches of major rivers and tributaries back-filled as sea level rises 

with retreat of continental glaciers. 


Subaerial erosion. 

Glacially scoured fea- 
tures being modified 
by weathering, erosion, 
and deposition. 



In the Sacramento \'alley, water for irrigation, pub- 
lic supply, and indu.stry is obtained primarily from 
surface-water sources, but in part from wells. These 
wells, in general, range in depth from 100 to about 
500 feet, although some wells are as much as 1,000 
feet deep. Most wells of large capacit\- are used for 
irrigation or for public supply; their \'ields range from 
200 to 2,000 gpm (gallons per minute). Estimated 
withdrawal of ground water for irrigation in the Sac- 
ramento \'alley during 1964 was on the order of 
2,400,000 acre-feet. This represents an increase of 85 
percent from the estimated withdrawal of about 
1,300,000 acre-feet in 1950 (Olmsted and Davis, 1961, 
p. 8). The estimated total storage capacity of the de- 
posits in the 20- to 200-foot depth range is about .3.3'/, 
million acre-feet. Ho\\ever, the flood-basin deposits 
are fine-grained silt and clay, and thus are not usable 
for c>'clic storage. Therefore, the total rechargeable 
storage capacit>- to a depth of 200 feet is about 28 
million acre-feet. 

Water levels in the Sacramento \'alley have not 
been drawn down e.xcessively b\- pumping. In most 
of the valle_\' water levels have not declined as much 
as 100 feet, and in some areas levels have been raised 
by seepage from surface-water irrigation. 

In the San Joaquin \'alley, water for irrigation is 
supplied both from surface-water sources and from 
wells, but probably about 60 percent is from wells. 
Well water is the sole suppl\' for half the irrigated 
land and a supplemental supply for another quarter. 



Furthermore, ground water supplies nearl\' all the mu- 
nicipal, industrial, and domestic needs. 

Depths of water wells range wideK', from 100 feet 
to 3,500 feet, depending either on the permeability^ 
of the deposits or on w ater-quality controls. For ex- 
ample, wells tapping the highl\' permeable alluvial-fan 
deposits derived from the Sierra Nevada granitic com- 
plex are relatively shallow. Accordingly, on the east 
side of the valle\-, from the Mokelumne River to the 
south edge of the Kings River fan, and within the 
Kern River fan, well depths range from 100 to 500 
feet and the average depth is onl\' about 250 feet. In 
contrast, on the central west side in western Fresno 
County, where the alluvial deposits of the Tulare 
Formation arc derived chiefly from sandstone and 
shale detritus of Coast Range origin, and the shallower 
ground water is of poor quality, wells range in depth 
from 500 to 3,500 feet with the average depth being 
about 1,500 feet. At the south end of the valley, south 
of the Kern River fan, well depths range from 600 
to 2,000 feet; the average is about 1,000 feet. 

Yields of irrigation wells in the San Joaquin \'alle\" 
also var\- widel\', ranging from 100 to more than 3,000 
gpm, but most wells \icld 500-1,500 gpm. Estimated 
storage capacity- of the deposits in the depth interval 
from 10 to 200 feet is 93 million acre-feet. Locally the 
reservoir has been dewatered to a depth in excess of 
350 feet. 

Estimated w ithdrawal of ground water for irrigation 
in the San Joaquin \'alle\- during 1964 was on the 






1966 



Poland and Evf.nson: Great \'alli.y 



243 




EXPLANATION 



OutI i ne of Val ley 

Drawn chiefly on boundary of 

consol idafed rocks 



Line of equal subsidence 

In feet, dashed where approx i mate 
interval variable 



California Aqueduct 
Under construct i on 

1926-62 

Peri od of vert ical control 

Compiled from leveling of the U.S. 
Coast and Geodetic Survey and 
Topographic mapping by U.S. 
Geolog I ca I Survey 



Figure 2. Areas of major land subsidence in the Greet Central Valley. 



CilOHK.^ 



NoKlllI UN C^ALIKORNIA 



Hul 



190 



order of 10,700,000 ;icrc-fcct, representing more than a 
threefold increase since 1940 \\ hen the draft was about 
} million acre-feet. This large withdrawal has caused 
substantial overdraft on the central west side and in 
much of tiie southern part of the \'alle\-, \\here re- 
plenishment is small compared to withdrawal. As a re- 
sult, water levels have declined 100 to more than 400 
feet in the confined aquifer s\stem in the Tulare 
Formation in western I'Vcsno Count\' and more than 
lOO feet in the same formation in Kern County south 
of the Kern River fan. 

LAND SUBSIDENCE 

In the great agricultural development of the Cen- 
tral \'alle\-, man has caused major subsidence of the 
land surface in three extensive areas between Sacra- 
mento and the south end of the \'alley. (See figure 2.) 
These three areas aggregate about 4,000 square miles, 
or roughl\- one-third of the valle\' lands south of 
Sacramento. Maximum subsidence ranges from H feet 
south of Bakersfield to 23 feet southeast of Los Banos. 
Nowhere else in the world has man produced such 
extensive subsidence of this magnitude. 

The subsidence is of three t\pes. In the low lands 
of the Delta at the confluence of the Sacramento and 
San Joaquin Rivers, subsidence has been caused chiefl\ 
b\- the oxidation of peat lands accompan\ing drainage 
and cultivation. In the largest area, between Los Banos 
and Wasco, and at the sf)uth end of the valley between 
Arvin and Maricopa, most of the subsidence has been 
caused b\' lowering of the artesian head in confined 
aquifer systems, due to the intensive pumping of 
ground water. Locall>', on the west and south flanks 
of the valley, a third t\pe of subsidence has been 
caused by near-surface compaction of moisture-defi- 
cient alluvial-fan deposits above the water table, after 
initial wetting by percolating irrigation water. This 
third type of subsidence is of such local extent that 
it cannot be shown on figure 2. 

Subsidence of the Delta 

The organic soils or peat lands at the confluence of 
the Sacramento and San Joaquin River systems are 
highl\' productive agricultural lands. Drainage for cul- 
tivation began in 1 H50 and development continued for 
the next 70 years. The Delta is now a complex svstem 
of islands and channels, and prior to reclamation the 
islands were approximately at mean sea level. Levees 
were constructed around the islands at the time of 
their reclamation, and as the islands have subsided 
farther and farther below sea level the maintenance 
of levees and channels has been an increasinglv diffi- 
cult job. 

The generalized lines of equal subsidence shown on 
figure 2 were constructed from topographic maps of 
the Geological Survev based on field surveys in 1952. 
The subsiding area covers about 450 square miles and 
more than one-third of the island area was 10 to 15 
feet below sea level in 1952. The peat ranges in thick- 
ness from near zero to more than 40 feet. 



Weir (1950) studied the subsidence in the Delta 
area for about 35 \'ears, beginning in 1922. He found 
that subsidence on one island ( Mildred Island) w as 9.29 
feet from 1922 to 1955, and was relativelv uniform, 
averaging 0.2H foot per \ear. He concluded that the 
causes of the subsidence were: oxidation, compaction 
bv tillage machinery, shrinkage by drying, burning, 
and wind erosion. Stephens and Johnson (1951) 
studied a similar peat subsidence in the Florida F-ver- 
glades and concluded riiat the principal cause was oxi- 
dation due to action of aerobic bacteria above the 
water table. Hence, the primar\ cause of the Delta 
subsidence is the lowering of the water table by drain- 
age in order to grow crops. 

The sediments beneath the peat also have subsided 
to a much lesser degree, possibly because of extraction 
f)f gas and water from major local gas fields. 

Near-Surface Subsidence 

Locally on the west and south flanks of the San 
Joaquin \'alley, near-surface alluvial-fan deposits 
above the water table have subsided in response to the 
first irrigation of the land. In the Los Banos-Kettleman 
City area, this near-surface subsidence or hydrocom- 
paction encompasses two areas 4 to 6 miles wide and 
aggregating 22 miles in length along the west edge of 
the valley. Along the southwest flank of the vallev 
between Lost Hills, Maricopa, and Wheeler Ridge, are 
four areas susceptible to near-surface subsidence; these 
aggregate at least 40 miles in length. 

The deposits susceptible to hvdrocompaction have 
been moisture deficient ever since their deposition. 
W'hen water is applied to them the cla\- bond is weak- 
ened and the deposits compact (Bull, 1964). Subsi- 
dence of 5 to 10 feet is common and locally as much 
as 15 feet has been observed. This type of subsidence 
poses a serious problem in the construction and main- 
tenance of large canals, irrigation distribution systems, 
pipelines, powerlines, highways, and buildings. The 
California Aqueduct (fig. 2), now under construction, 
passes through about 60 miles of these deposits be- 
tween Los Banos and Wheeler Ridge. As a prevent- 
ative measure the susceptible deposits along the Aque- 
duct alignment are being precompacted bv prolonged 
basin-t\pe wetting prior to the placing of the con- 
crete lining. 

Subsidence Due to Water-Level Lowering 

The areas of significant land subsidence related to 
water-level lowering are in the San Joaquin \'alley. 
The two areas of major extent are outlined on figure 
2. The larger area extends about 145 miles southeast 
from Los Banos to Wasco, and includes about 3,300 
square miles within the 1-foot subsidence line. The 
smaller area south of Bakersfield includes about 450 
square miles. Together these areas cover about one- 
third of the San Joaquin \'alle\-. The subsidence has 
been greatest at three centers. The center of maximum 
subsidence is 7 miles west of Mendota where 23 feet of 
subsidence has occurred (1963); the maximum rate of 



1966 



Poland and Evenson: Great Valley 



245 



subsidence from 1959 to 1963 was about 1.5 feet per 
year. A second center is 2 miles north of Delano 
where 12 feet of subsidence has occurred, but sub- 
sidence has almost ceased there because of recovery' 
of \\'ater levels. The third center, 18 miles south of 
Bakersfield, has subsided 8 feet. 

These areas of land subsidence overlie confined 
aquifer systems, in which the artesian head has been 
drawn down everywhere more than 100 feet and as 
much as 400 feet locally north of Kettleman City. 
The area between Los Banos and Wasco is almost 
wholly underlain by the Corcoran Clay Member of 
the Tulare Formation which confines the underlying 
productive aquifer system that is also in the Tulare 
Formation. 

The relationship of subsidence to head decline near 
the three centers of subsidence is illustrated by figures 
.3, 4, and 5. Figure 3 shows the nearly parallel trends 



'v^ ,'?'"*•''. 




Figure 3. Subsidence and change in artesian head in an area 
8 miles southwest of Mendota, Fresno County. 

of bench-mark subsidence and artesian-head decline 
from 1940 to 1963 at a site 8 miles southwest of Alen- 
dota. In this 22-year period, the bench mark subsided 
about 18.5 feet and the artesian head in nearby \\ells 
tapping the confined aquifer system decreased about 
260 feet. The ratio of subsidence to head decline was 
approximately 1:20 from 1940 to 1950 and 1:10 from 
1950 to 1963. This increase in the ratio with increasing 
drawdown of artesian head is characteristic of much 
of the subsiding area. It suggests a cumulative in- 
crease in delayed compaction of the fine-grained 
interbeds as head declines, due to slow adjustment of 
pore pressure. 

Five miles northeast of Delano, artesian head de- 
clined continuously from 1930 to 1951 (fig. 4) and 
then recovered rapidh- as a result of delivery of sur- 
face water for irrigation from the Friant-Kern Canal, 
which brings water south from the San Joaquin River. 
Nearby bench marks showed a parallel subsidence into 
the early 1950's, after which the rate of subsidence de- 
creased in response to the recovery of artesian head. 

The relation of subsidence to artesian-head decline 
21 miles south of Bakersfield (about 5 miles northwest 
of the town of Wheeler Ridge) is shown on figure 5. 
The water level declined from about 130 feet below 
the land surface in 1946 to 415 feet below in 1962, at 



I I I I I I I I I 1 I I I I I I I I I ' I I I I I I 




Figure 4. Subsidence 
ern County. 



and change 



an average rate of 18 feet per year. From 1947 to 1953 
the rate of subsidence of nearby bench mark A-303 
was 0.16 foot per year and during 1959-62 was 0.30 
foot per year. At this site, therefore, the ratio of sub- 
sidence to artesian-head decline increased from 1:112 
(1947-53) to 1:60 (1959-62). 

To determine how much of the subsidence is caused 
by compaction of the deposits tapped b\' water wells, 
and to investigate the character of the response of the 
sediments to increasing effective stress (decreasing 
artesian head), the U.S. Geological Survey has estab- 
lished depth bench marks and operated compaction 
recorders in about 30 unused wells or cased core holes. 
The compaction-recorder installation (fig. 6) furnishes 



f 2.0 



y^Bench ma r K A-303 




Well 11 N -;aw - gA I 



I I I I I I I I I I I M I I I I I I II I I I I I 



Figure 5. Subsidence and ortesion-he 
field. After Lofgren {1963, fig. 47.3) 



450 
Bokei 



246 



Gfoi-OCY of Northirn Cai.ifornia 



Bull. 190 




Metal table on 
<■ concrete platform 



■ Cable clamp 



Well casing 



Plastic -coated 
cable, "^-inch. 
stranded 



Anchor weight 
200 to 300 lbs" 



Open hole 



Figure 6. Diagram of typical compaction-recorder installation. 



continuous measurement of compaction occurring be- 
tween the land surface and the depth bench mark at 
the well bottom. 

The first compaction recorder of this t\pe was in- 
stalled in a well 2,030 feet deep near Huron in 1955. 
Figure 7 shows the record of compaction from 1956 
into I960, the subsidence of nearb\- surface bench 
mark B 889 as determined by precise leveling of the 
U.S. Coast and Geodetic Survey, and tiie fluctuation 
of artesian head in a nearb\- well. During the 4.8 years 
of record shown, measured compaction of the aquifer 
s_\stem to a depth of 2,030 feet was 3.8 feet, the land 
subsided 4.6 feet, and artesian head declined about 40 
feet. Tiius, the measured compaction was 82 percent 
of the subsidence, indicating that 0.8 foot of compac- 
tion occurred below 2,030 feet, \\hich is reasonable 
because nearby wells withdraw water from greater 
depths. The rate of compaction is variable, being 
greatest during periods of rapid decline in artesian 
head; recovery of head results in decrease or cessation 
of compaction. Such evidence, obtained here and at 
many other sites, indicates that the aquifer s_\stem is 
extremely sensitive to change in effective stress as de- 
fined by change in artesian head. At one site, increase 
of about 1 percent in effective stress (a 5-foot lower- 
ing of artesian head) caused noticeable compaction. 

At a site near the town of Cantua Creek, a compac- 
tion recorder installed in a 2,000-foot well (Nl) in 
1958 recorded 7.43 feet of compaction by the end of 
1964 (fig. 8). Two shallower installations registered 




340 
360 
380 


\A f 


A A h 


k\ r\ 


/- 




\ 


\h 


^ V 


\r. 


\a 


v 


V \J 


\y 


\ 


v\ 


420 




Hydro 


gr apti of sei 1 ^ 
19 I6-27MI 


^ \7 


V 










V 















Figure 7. Measured subsidence, compaction, and water-level change, near Huron, Fresno County. After Lofgren 
(1961, fig. 24.2). 



1966 



Poland and Evenson: Great Valley 



247 



N3 N2 Nl 



bed 

C on ( I ne d 
aquifer 
" system 





1 95B 


1 959 


1 960 


1 961 


1 962 


1 963 


1 964 




- 



















^x.^ 


-^ ^ 












^- 




■ — 








^ 










■^fcw 


"- 








v^ 










f 


— 






^■^^^ 








— 


-" 


- 


compaction 

lecoidec Deptli 

•sti (Foot) 

16 15-34111 2.000 

34N2 703 

34H3 500 




^ 








o 

a. 
o 






^^ 




- 




- 


1 










^^^ 



A. Re lat ion of well depths 
to hydr ol ogle un I ts 



Figur 



B. Measured compaction 

8. Compaction in three wells near Cantua Creek, Fresno County, during 1958-64. 



0.89 foot (N3; 500 feet deep) and 2.10 feet (N2; 703 
feet deep) of compaction during the same period. If 
the distribution of compaction in the interval between 
the bottoms of wells N3 and N2 was uniform, about 
17 percent of the measured compaction occurred 
above the principal confining bed and 83 percent in 
the confined aquifer system. The measured compaction 
to 2,000 feet (well Nl) from February 1960 to Alarch 
1963 was 3.37 feet; subsidence measured by leveling 
to surface bench marks in the same period was 3.45 
feet. Thus, the measured compaction to this depth 
accounted for about 98 percent of total subsidence. 
It is noteworthy that the rate of compaction has been 
about constant throughout the year, even though the 
artesian head in an adjacent well fluctuates 60 feet or 
more seasonally. This suggests that at this site the 
residual excess pore pressure in the fine-grained inter- 
beds is much greater than the annual fluctuation of 
head. 

In conclusion, decrease in artesian head in compres- 
sible confined aquifer systems results in increased effec- 
tive stress (grain-to-grain load) on the confined sedi- 
ments and they compact, causing land subsidence. The 
magnitude of the subsidence is dependent on the mag- 
nitude of change in head and on the compaction char- 
acteristics and thickness of the sediments. The greater 
the number of clayey interbeds in the system, the 
greater is the compaction. Continuous measurements 
of compaction indicate rapid response to head change 
at most places in these subsiding areas. Subsidence can 
be slowed down or stopped by a rise in the artesian 
head sufficient to eliminate residual excess pore pres- 
sures. However, the compaction is almost entirely 
permanent. Recovery of water levels has not caused 
appreciable recovery of the land surface in an_\' of 



the areas studied. This has been demonstrated on a 
broad scale in the Delano area. 

REFERENCES 

Bull, W. B., 1964, Alluvial fons and near-surface subsidence in western 
Fresno County, Calif.: U.S. Geol. Survey Prof. Paper 437A, p. 
A1-A71. 

Davis, G. H., Green, J. H., Olmsted, F. H., and Brown, D. W., 1959, 
Ground-water conditions and storage capacity in the San Joaquin 
Valley, California: U.S. Geol. Survey Water-Supply Paper 1469, 
287 p. 

Davis, G. H., Lofgren, B. E., and Mack, Seymour, 1964, Use of ground- 
water reservoirs for storage of surface water in the San Joaquin 
Valley, California: U.S. Geol. Survey Water-Supply Paper 1618, 
125 p. 

Davis, S. N., and Hall, F. R., 1959, Woter quality of eastern Stanislaus 
and northern Merced Counties, California: Stanford Univ. Pub. Geol. 
Sci., V. 6, no. 1, p. 1-112. 

Evernden, J. F., Savage, D. E., Curtis, G. H., and James, G. T., 1964, 
Potassium-argon dotes and the Cenozoic mammalian chronology of 
North Americo: Am. Jour. Sci., v. 262, p. 145-198. 

Jando, R. J., 1965, Quaternary alluvium near Friant, California, in 
Internot. Assoc, for Quaternary research, Vllth Congress, Guide- 
book for field conference I, Northern Great Basin and California, p. 
128-133. 

Lofgren, B. E., 1961, Measurement of compaction of aquifer systems 
in areas of land subsidence: Art. 24 in U.S. Geol. Survey Prof. Paper 
424-B, p. B49-B52. 

1963, Land subsidence in the Arvin-Maricopa area, Calif.: Art. 47 

in U.S. Geol. Survey Prof. Paper 475-B, p. B171-B175. 

Olmsted, F. H., and Davis, G. H., 1961, Geologic features and ground- 
water storage capacity of the Sacramento Valley, California: U.S. 
Geol. Survey Water-Supply Paper 1497, 241 p. 

Piper, A. M., Gale, H. S., Thomas, H. E., and Robinson, T. W., 1939, 
Geology and ground-water hydrology of the Mokelumne area, Coli- 
fornia: U.S. Geol. Survey Water-Supply Paper 780, 230 p. 

Stephens, J. C, and Johnson, Lamar, 1951, Subsidence of organic 
soils in the Upper Everglades region of Florida: U.S. Dept. Agr., 
Soil Cons. Service, 16 p., 25 figs. 

Weir, W. W., 1950, Subsidence of peat lands of the Sacramento-San 
Jooquin Delta, California: California Univ. Agr. Exp. Station, Hil- 
gardia, v. 20, no. 3, p. 37-56. 



248 



GKOLOCiY OF NORTIIKRN CaIJKORMA 



Bull. 190 




conditions at Michvay. Rush of teams with material for rigs on claims located under placer law. Photograph by R. B. Moran. 



ECONOMIC MINERAL DEPOSITS OF THE GREAT VALLEY 



Bv Earl W. Hart 
California Division of Mines and Geology 



Of more than 50 different mineral commodities pro- 
duced in California, only 15 are current!)- exploited 
in the Great Valley, and the valley is generally tiiought 
of in terms of its agricultural rather than mineral 
wealth. Nevertheless, the province yielded $489,250,- 
000 worth of minerals in 1964, which was 31 percent 
of the State's total mineral production. Table 1 shows 
that petroleum fuels — petroleum, natural gas, and 
natural-gas liquids — constitute 90 percent of the min- 
eral production of the province. Sand and gravel make 
up nearly 9 percent of the total and the 1 1 other com- 
modities account for the rest. 

The economic importance and geologic occurrence 
of the various mineral commodities are discussed 
briefl\- below. The oil and gas fields and the more sig- 
nificant mineral deposits, which are mainly those that 
are being utilized, are shown on the map (fig. 1 ). For 
more detailed data on the mineral deposits, the reader 
is referred to U.S. Geological Survey (in press), 
Wright (1957), and many other publications of the 
California Division of Mines and Geology, California 
Division of Oil and Gas, U.S. Geological Survey, and 
U.S. Bureau of Mines. , 

Table 1.— Mineral production in ihe Great Valley in J964. 





Mineral 


Production' 


Rank 


Quantity 


Value 


1 

2 
3 
4 

5 
6 
7 


Petroleum bbls 

Natural gas ....l.OOOcu ft 
Sand and gravel short tons 
Natural-gas liquids 

1,000 gals 
Gold 

Gypsum short tons 

Clay short tons 

Unapportionedf (gold, peat, 
coal, pumicite, carbon 
dioxide, stone, platinum, 
silver, gemstones) 

Total-. Great Valley 
Total California 


123,683,000 

414,296,000 

27,830,000 

401,291 

838,000 
447,000 


?299,98 1,000 
123,876,000 
34,131,000 

26,020,000 

1,472,000 
1,289,000 

2,481,000 






8489,250,000 
?1,560,510,000 



1 Based on data collected by the U. S. Bur. Mines. 

• Concealed under unapportioned to avoid revealing the production of individuals. 

t Listed in approximate order of decreasing value. 

PETROLEUM 

Virtually all of the petroleum (or crude oil) is pro- 
duced from fields of the San Joaquin Valley, which 
comprises the southern half of the Great Valley. The 
so-called San Joaquin basin yields 335,000 barrels of 



oil per day, or 41 percent of California's production. 
Most of the oil comes from sand and, to a lesser extent, 
fractured shale reservoirs of Cenozoic (mainly Mio- 
cene and Pliocene) formations. A substantial amount 
of oil also is obtained from fractured schist of pre- 
Cretaceous age. Upper Oetaceous sands \ield very 
little oil. Comulative oil production to January 1, 1965, 
is more than SVz billion barrels, and proven oil re- 
serves are about 2 billion barrels. "Giant" oil fields, 
with more than 100 million barrels of cumulative pro- 
duction, are listed in table 2. 



Table 2.— Oil fields of Ihe Great Valley with cumulative 
production greater than 100 million barrels of oil. 


Fields 


Cumulative 

oil production, 

in barrels, 
through 1964 




947,891,000 




549,931,000 




524,291,000 




440,395,000 




408,523,000 




393,479,000 


ElkHills 


271,471,000 




149,464.000 




124,270,000 




112,566,000 




109,402,000 




105,937,000 




105,096,000 







NATURAL GAS 

A large quantity of "wet" natural gas is produced 
from oil reservoirs in the San Joaquin \'alley. More 
than half of this wet gas, after extraction of natural- 
gas liquids, is returned to the oil fields to maintain 
reservoir pressures; the balance is marketed or other- 
wise used. "Dry" natural gas, on the other hand, is 
obtained from gas reservoirs in which oil is not pres- 
ent. Such gas occurs mainl\' in the Sacramento Valley 
and northern San Joaquin Valley, but a fe\\' important 
gas fields lie close to the oil fields of southern San 
Joaquin \'alley. The dry gas comes from sands of Late 
Cretaceous and Tertiary age. In 1964, net production 
of drv and wet natural gases respectiveh' amounted to 
166 and 248 billion cubic feet for the Great Valley. 
Combined, this is 62 percent of the State's gas produc- 
tion. Natural gas reserves as of December 31, 1964 are 
estimated at nearl>' 7.5 trillion cubic feet, about 55 
percent of which is wet gas. Onl\- six dry gas fields 



250 



Geology ok Northi-rn Cai.i forma 



Bull. 190 



y^^ SHASTA 



V 



\ 



\ 



V 



•.r 



At 



^ 'butte. 



NATURAL CAS 

40. A t buck le 

41. Bunke r 

42. 6r I mes 

43. Gr ifflss tes t 

44. L«lh( op 

45. McMu I I in Ranch 

46. R i Vista 

47. R I ve r Island 

48. Su i sun Bay 

49. Sut le r But t as 

50. Suttar City 

51. Thor nt on «es t - 

la Inul Gr ova 

52. Tr ico 



r" 



n 



53. Va 

54. «l 



^ t-^-\ 



Id Goose 
55. W I I I ois-Beeh i 



It Bend 



CLAY 

1. Buana Vista 

2. Eice I 

3. I one 

4. Lincoln 

5. Va I lay Spr I n 

COAL 

6. lone 

GOLD 

Ma in dredge I ie Ids 

7. But t e Creek 

8. Camancha 

9. Cot t oniood Creek 
10. F I som 

I t. Hammon t on 
I 2. La Gr ange 
I 3. Ml ch I gan 
I 4. Or ov I I la 
1 5. Sna I I ing 

GYPSUM 

I 6. Buana Vista Lake 

1 7. Los t Hills 

PEAT 

1 8. Sac r amen t San JoaquI 

Delta area 

PUMIC I TC 

19. F r i a n t 

SAND ANO GRAVEL 

2 0. Ainerican Rivar 

21. Cache Creek 

22. Corral Hollo* Creak 

23. Kawaah River 

24. Ka r n River 

2 S. Kings River 

26. Los Ban os Creek 

27. Los Gat OS Creek 

28. Me r ced River 

29. Moke I unne River 

30. Sacrananlo River 
3I.Sacraaento River 
32. San Emlgdio Creek 

33. San Joaquin River 

34. S t an i c I aus River 

35. St ony Creek 

36. Tu le River 

37. Tuo I uane River 

3 8. Tuba River 

SPECIALTY SANO 
39. I one 



OLUSA iV" ! "(^ 

^SOLANO I ."i^^ACRAI^ENTo!) 



.^'"•"S%° „20®\ 



~^> 



U-.^,-<^;jl8 SAN \ I 

VjV '-!•? « JOAQUIN [\\ 

^^^s W » i A 

V STANISLAUS ^'^ 

\ ■ 



OIL 

56. As pha I I 

ST. Belgian Aniiclina 

58. Be I r i dge South 

59. Br en I nood 

6 0. Buena V I s 1 1 

61. Cost ord 

62. Coa I I nga 

63. Coalinga East Eitensi 

64. Gu i ja r r a I Hills 

65. Coles Levee North 
6 8. Cynir i c 

6 7. Edison 
6 8. E I k Hills 

6 9. Fr u i t va la 

7 0. Greeley 

71. He r n Front 

72. kern R i ver 

73. Ket t leiean Nor Ih Ooiae 

74. Los I Hills 

75. McAit tr ick 

76. Mi d«ay-Sunsat 

77. Moun t Poso 

78. Poso Creek 
7 9. Rio Bravo 

60. Round Moun tain 

81. San Enid i Nose 

82. Te j on North 
63. Whee I e r Ridge 



(Redd Ing) 
(Red Bluff) 




Figure 1. Mop of the Greot Valley, showing the location of the principal economic mineral deposits. 



1966 



Hart: Grkat V'allky 



251 



have yielded more than 100 billion cubic feet of gas; 
these are listed below: 



Fields 


Cumulative 

gas production, 

in 1,000's of cu ft, 

through 1964 




2,264,283,942 




179,059,716